Marcie started working a part-time job at the beginning of the summer. After four weeks, she increased the number of hours she worked each week by 1/5. After another four weeks, she decreased the number of hours she worked each week by 1/3. From then on, she worked 20 hours weekly. How many hours was she working each week when she began working at the beginning of the summer?

(A) 5
(B) 10
(C) 16
(D) 25
(E) 30

Answer: D

Source: EMPOWERgmat