Question

How do I solve literal equations? 

Ex. P=2(a+b) solve for b

Answer 1

Sounds like rearranging to me:

P=2(a+b) -- expand brackets
P=2a+2b -- subtract 2a
P-2a=2b -- divide by 2

b=(P-2a)/2

Answer 2

$P=2(a+b)\\ P=2a+2b\\ 2b=P-2a\\ b=\frac{P-2a}{2}$