Is it permissible for someone to give a friend 12,0 [currency units] to buy a car that is government-subsidized (out of 15,0, the government agency pays 3,0), and then the friend sells it to him at an agreed-upon price, knowing that the government agency does not prohibit this?

This transaction between the employee and his friend is forbidden and invalid because the amount paid by the questioner to the employee is a loan that brings benefit (the purchase of the car), thus it is considered usury (riba). This is due to its violation of the intent of Islamic law regarding lending, which is benevolence, not the lender's profit. Therefore, every loan that brings benefit is usury. The Prophet, peace and blessings be upon him, forbade lending and selling, and accepting a gift or riding a mount from someone whom one has lent money to.