Answer:
b = (p -2a)/2
Explanation:
You want b the subject of the relation p=2a+2b.
Solution
Solve this the way you would solve any 2-step linear equation.
p = 2a +2b . . . . . . given
p -2a = 2b . . . . . . . subtract the term not containing b
(p -2a)/2 = b . . . . . . divide by the coefficient of the variable
Your formula is ...
b = (p -2a)/2
or
b = (p/2) -a