Answer:
[tex]a = 2b - x[/tex]
Step-by-step explanation:
[tex]2(x + a) = 4b \\ 2x + 2a = 4b \\ 2a = 4b - 2x \\ \frac{2a}{2} = \frac{4b - 2x}{2} \\ a = \frac{2(2b - x)}{2} \\ a = 2b - x[/tex]
