X Wished to Purchase a Motor Vehicle from Y on Credit

X wished to purchase a motor vehicle from Y on credit, but X was unemployed, and Y was hesitant to sell to him for that reason. Z, who was quite wealthy, said to Y: "Sell X the automobile on credit, and if X does not pay you, I will." If Z made the guarantee in writing, and signed the document, the guarantee would not be enforceable until X defaulted on a demand for payment by Y.