You are correct. The answer is choice C.
Explanation:
We can solve for 'a' like so
[tex]A = \frac{(a+b)}{2}h\\\\2A = (a+b)h\\\\\frac{2A}{h} = a+b\\\\\frac{2A}{h}-b = a\\\\a = \frac{2A}{h}-b\\\\[/tex]
In the second step, I multiplied both sides by 2. Afterward, I divided both sides by h in the third step. Lastly, I subtracted b from both sides to isolate 'a' in step 4. Each step is following PEMDAS in reverse to undo every operation done to variable 'a'.
