I'm not completely sure about this one, but I've got an answer :P
b4=12 first you have to leave b by itself, so the positive 4 becomes negative as it switches sides.
b=12-4 subtract 12 and 4 from each other
b=8 the variable 'b' is 8
You need to find b13, and in order to find that you need to plug in the 8 where the b is
(8)13 in the next step you have to multiply both 8 and 13
8(13)=104
Hope this helps
