Noelle walks from point A to point B at an average speed of 5 kilometers per hour. At what speed, in kilometers per hour, must Noelle walk from point B to point A so that her average speed for the entire trip is 8 kilometers per hour? Pick: A) 6.75 B) 7 C) 7.25 D) 7.5 E) 20

Rationale: "let ' s suppose that speed while returning was xkm / h since the distance is same , we can apply the formula of avg speed avg speed = 2 s 1 s 2 / s 1 + s 2 8 = 2 * 5 * x / 5 + x x = 20 e is the answer"
Answer: E