To reach the second floor you would look at all ways to enter to building(8) and multiply it by the number of ways to reach the second floor (12).
8 x 12 = 96 possibilities
Think of it in groups.
1st door and 12 possible sets of steps 2nd door and 12 possible sets of steps 3rd door and 12 possible sets of steps 4th door and 12 possible sets of steps 5th door and ..., etc.....
