How long will it take them before both cars reach the starting point again simultaneously?

Cory and Melissa are racing electronic cars around a circular track. They begin at the same time going in the same direction. Cory’s car completes a revolution in 40 seconds, while Melissa’s car completes a revolution in 35 seconds. How long will it take them before both cars reach the starting point again simultaneously?

How do you trade cars from owner to owner if both owners have loans on their current cars?

Basically what the question says…
I own a car and the other woman owns a car. We want to trade cars but we are both making payments to the bank at the moment on our current cars. Is there any way to trade our cars that we have?