Anyone know how to do this?? Help pls

Answer:
The correct answer is A. a = 2s - b - c
Step-by-step explanation:
First you multiply 2 on both sides and you will end up with 2s = a + b + c.
Then to isolate a you would subtract both b and c from both sides of the equation as well to end up with your answer of a = 2s - b - c.