Answer :
Remember your order of operations . . . multiplication/division comes before addition/subtraction.
A = a + (b/2)
Subtract 'a' from each side: A - a = b/2
Multiply each side by 2 : 2(A - a) = b
A = a + (b/2)
Subtract 'a' from each side: A - a = b/2
Multiply each side by 2 : 2(A - a) = b