IF I remember my math correctly:
There can be any one of four cars first (4)
then there can only be three come in second x3
leaving two to come in second x2
then the loner x1
so 4x3x2x1= 24 possible combinations
There can be any one of four cars first (4)
then there can only be three come in second x3
leaving two to come in second x2
then the loner x1
so 4x3x2x1= 24 possible combinations