Question: In a restaurant, guests can choose among 3 starters, 5 main dishes and 4 desserts. How many possibilities exists to order a menu?

If a problem can be divided into 2 subproblems which are executed one after another, and if there are n possibilities for the 1st subproblem and m possibilities for the 2nd subproblem, then there are n*m possibilities in total.

There are 3 routes from Gummersbach to Cologne and 4 routes from Cologne to Aachen. Then there are in total 3*4 = 12 possible routes from Gummersbach to Aachen.