-3.132 is the answer, you just had to multiply all of them one at a time (:
notice, this will just be a Permutation.

you can always check your calculator also for a [ ₙPᵣ ] button.
You are missing crucial bits of information. If you could reply with the missing information, I will do my best to assist you :)
The top later is 5 because if the ladder is 10 inches half is 5 and the other half is 5