Verified Answer :

p = 2 (a + b)   Use the Distributive Property
       p = 2a + 2b   Subtract 2a from both sides
p - 2a = 2b   Divide both sides by 2
\(\frac{p - 2a}{2}\) = b   Switch the sides to make it easier to read
      b = \(\frac{p - 2a}{2}\)