Dan agrees to sell a second$-$hand motor car to Joe for R$50000.$ The parties agree that Sam will put new tyres on the car and conduct a mechanical check up on the car, and that Ben will transfer the purchase price at the end of the week. Later that day, Sam$$s nephew takes the car on a joy ride and negligently collides with a bus, the car is damaged beyond repair. Determine whether the contract concluded between Dan and Joe is a valid contract. Provide reasons for your answe