total capacity of the room is x/4=60, hence x=240. we need to fill up the 2/3 capacity of the room. that means (2/3)*240=160 boxes. we store 5 boxes each hour and 3 boxes are supplied each hour. hence the net number of boxes stored each hour is 2. we already have 60 boxes in the room and need additional 100 boxes (because we need total 160 boxes stored). at the rate of 2 boxes per hour we will need 50 hours to store additional 100 boxes. so answer C is the right answer.