15 ! : as a punishment for something naughty that we did, my little brother and i have to whitewash both sides of a fence. we start at the same time, and we each work at a constant rate. if we each whitewash one side, i'll finish in 2 hours and my brother will finish in 3 hours. but i'm a nice kid, so after i finish my side, i go around to the other side and my brother finish his side. from the time i start him, how many minutes does it take us to finish the job?