Answer:
Neither Is correct
Step-by-step explanation:
Sarah just added all four sides of the rectangle. She added 3x+3x+(x+7)+(x+7), which is a correct way to find the perimeter. What she did wrong, though, is not adding all the x's together, she only added the 3x, but not the lone x's.
John, on the other hand, had a good start but not the greatest finish. He also started out correct, by multiplying the 2 "3x's" and the 2 "(x+7)'s". It's basically doing what Sarah said, but multiplying. But what he did wrong was not distributing the 2 to the (x+7) properly.
He did this: 2(x+7)=2x+7
But what he should have done is this: 2(x+7)= 2(x)+2(7) (distributing the x to every term, including the seven), which gives you 2x+7, by which adding the 6x after gives 8x
