Is the transaction permissible in which a person pays 20,0 to another for the purchase of a car worth 60,0, on condition that the buyer leases it to a company for 2,0 and gives the payer one-third of the profit, with a guarantee of the return of the capital (20,0) by check if they wish to withdraw from the partnership?

This transaction is not valid because it is closer to a loan with interest, which is a corrupt and impermissible contract. The correct approach is for you to be a partner in the car, bearing your share of the risk and benefiting from its gain. Your partner does not guarantee your capital, nor is he obligated to buy your share of it at the price you paid.