Start by multiplying everything out on the right side.
A=1/2hb+1/2hB
Move things around so that you get the clump with "b" in it alone on a side.
A-1/2hB=1/2hb
Start to isolate b.
(A/h)-1/2B=1/2b
(2A/h)-B=b
The answer is b=(2A/h)-B. You don't need the parenthesis, just put the thing in the parenthesis into one fraction.
Hope this helps!
