Answer:
Step-by-step explanation:
I'm not sure if the right side is [tex]\frac{a + b}{2}[/tex] or [tex]a + \frac{b}{2}[/tex], so I'll provide an answer for both:
[tex]A = \frac{a + b}{2}[/tex]
[tex]2A = a + b[/tex]
[tex]2A - a = b[/tex]
[tex]A = a + \frac{b}{2}[/tex]
[tex]A - a = \frac{b}{2}[/tex]
[tex]2(A - a) = b[/tex]
[tex]2A - 2a = b[/tex]