permutation problem-four main highways

Question

There are four main highways from A to B and three from B to C. In how many ways may one drive from A to C and return, going through B on both trips without travelling on the same road twice?

Can't understand the logic. Can someone give me a hint?

Answer 1

You should consider how many choices you have at each step and use the multiplication principle. When you go from A to B you have four, but coming back you can't use the one you took before.