Question

If P=2a+b,express b in terms of P and A

Answer 1

This is accomplished by bringing b in one side and the other terms and variables in the other side.
Just like that:
\[P=2a+b\]
\[P-2a=2a+b-2a\]
\[P-2a=b\]
\[b=P-2a\]

Answer 2

Thank you for the medal!