What is the ruling on profits resulting from a partner's use of the company's car and showroom, where he works, to promote the partnership's goods, and how can this money be disposed of?

If your friend was authorized to promote his goods and use the car, then there is no blame upon you for taking the profit. However, if he was not authorized, then his action is forbidden, and he must pay rent to the owners of the exhibition and the car. The resulting profit is lawful if the rent is paid or the liability is discharged.