Please help me with this question. What formula would you use to find the missing lengths of the right triangles?

a2 + b2 = c2 can be use to find missing lengths of the right triangles

c.

step-by-step explanation:

because first you have to add the 4x, 9x, and the 7x together and you get 20x and then you add the last numbers up and you get 5and then you put the subtraction sign in there and that's how you get the answer.

your answer would be 12