Solveit:
Remember: 1 car has a choice of only 3 spots. It can park in any of those 3 and there will be 4 parking slots remaining. So, it has 3 choices.
The next car can park in any of 4 slots.
,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, 3 slots.
,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, 2 slots.
,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, 1 slot.
So, we have: 3 X 4 X 3 X 2 X1=3 X 4!=72 Different ways that the 5 cars can be parked.