Only Forward and Right are allowed. How many ways are there of getting from A to B? You might like to start with a smaller square, and work up to this problem.
In a 1 x 1 square, there are two routes: FR and RF. In a 2 x 2 square, there are 6 - FFRR, FRFR, FRRF, RFFR, RFRF, RRFF.
Now try a 3 x 3 square.
The problem is to be able to predict how many ways there are from A to B in any size of square. You might like to try this problem before clicking on NEXT.