#include <iostream>
#include <unordered_map>
#include <string>

class PrivateMarket
{
public:
    int64_t m_troops_cost{ 0 };
    int64_t m_jets_cost{ 0 };
    int64_t m_turrets_cost{ 0 };
    int64_t m_tanks_cost{ 0 };

    int64_t m_troops_available{ 0 };
    int64_t m_jets_available{ 0 };
    int64_t m_turrets_available{ 0 };
    int64_t m_tanks_available{ 0 };

    PrivateMarket(std::unordered_map<std::string, int64_t>&);
    void convertOilToUnits(int64_t);
    int64_t bushelsNeededForAvailableUnits();
    int64_t calculateNetworth();
};

PrivateMarket::PrivateMarket(std::unordered_map<std::string, int64_t>& units)
    : m_troops_cost{ units["troops_cost"] }
    , m_jets_cost{ units["jets_cost"] }
    , m_turrets_cost{ units["turrets_cost"] }
    , m_tanks_cost{ units["tanks_cost"] }
    {}

void PrivateMarket::convertOilToUnits(int64_t oil)
{
    m_troops_available = (oil/40)*30;
    m_jets_available = (oil/40)*25;
    m_turrets_available = (oil/40)*25;
    m_tanks_available = (oil/40)*10;
}

int64_t PrivateMarket::bushelsNeededForAvailableUnits()
{
    int64_t troops_cost{ m_troops_available*m_troops_cost };
    int64_t jets_cost{ m_jets_available*m_jets_cost };
    int64_t turrets_cost{ m_turrets_available*m_turrets_cost };
    int64_t tanks_cost{ m_tanks_available*m_tanks_cost };

    return (troops_cost + jets_cost + turrets_cost + tanks_cost) / 35;
}

int64_t PrivateMarket::calculateNetworth()
{
    return (m_troops_available*0.5)
        + (m_jets_available*0.6)
        + (m_turrets_available*0.6)
        + (m_tanks_available*2);
}

int main(int argc, char *argv[])
{
    if (argc < 6)
    {
        std::cout << "Error - Provide amount of oil stocked.\n";
        std::cout << "Lowest Possible: Troops -> 77 Jets -> 103 Turrets -> 112 Tanks -> 315\n\n";
        std::cout << "ie. calculate [STOCKED_OIL] [TROOP_COST] [JET_COST] [TURRET_COST] [TANK_COST]\n";
        std::exit(1);
    }

    int64_t oil_stocked{ std::stoi(argv[1]) };
    int64_t troop_cost{ std::stoi(argv[2]) };
    int64_t jet_cost{ std::stoi(argv[3]) };
    int64_t turret_cost{ std::stoi(argv[4]) };
    int64_t tank_cost{ std::stoi(argv[5]) };

    // private market prices
    std::unordered_map<std::string, int64_t> pm_prices{
        { "troops_cost", troop_cost }, 
        { "jets_cost", jet_cost }, 
        { "turrets_cost", turret_cost }, 
        { "tanks_cost", tank_cost }, 
    };

    PrivateMarket pm{ pm_prices };
    pm.convertOilToUnits(oil_stocked);

    // bushels needed for available units
    int64_t bnfau = pm.bushelsNeededForAvailableUnits(); 

    std::cout << "\n------------------------------------\n"; 
    std::cout << "Private Market Generated" << '\n';
    std::cout << "Oil stocked: " << oil_stocked << '\n'; 
    std::cout << "------------------------------------\n"; 
    std::cout << "Units Generated" << '\n';
    std::cout << "Troops: " << pm.m_troops_available << '\n'; 
    std::cout << "Jets: " << pm.m_jets_available << '\n'; 
    std::cout << "Turrets: " << pm.m_turrets_available << '\n'; 
    std::cout << "Tanks: " << pm.m_tanks_available << '\n'; 
    std::cout << "Bushels required to buy out PM: " << bnfau << '\n';
    std::cout << "Increase in Networth: " << pm.calculateNetworth() << '\n';
    std::cout << "\n";
}

Or use: https://www.onlinegdb.com/cSravmannf
Look at the arguments at the bottom to use your own numbers.

It's labeled: "Command line arguments:"

The order is such:
[STOCKED_OIL] [TROOP_COST] [JET_COST] [TURRET_COST] [TANK_COST]

Example output:
------------------------------------
Private Market Generated
Oil stocked: 60000000
------------------------------------
Units Generated
Troops: 45000000
Jets: 37500000
Turrets: 37500000
Tanks: 15000000
Bushels required to buy out PM: 464357142
Increase in Networth: 97500000

NOTE: You may have to scroll up to see this output in output window.

Thank you Celphi :-)