In a store room, one group of staff members fill the store with boxes and the other group of staff take the boxes from the store and supply them to the market. The boxes are stored at the rate of 5 boxes per hour whereas they are supplied at the rate of 3 boxes per hour. If the room is 1/4 filled with 60 boxes, in how many hours it will be 2/3 filled?β

A.) 20 hours
B.) 30 hours
C.) 50 hours
D.) 80 hours
E.) 120 hours

(Answer given is C but I highly doubt it. So, any help is appreciated.)