Buddy and Ken can do work 2/3 times faster than Tom and Ron. The LCM (10, 15) is 30. In thirty minutes Buddy and Ken will have installed 3 panels, while Tom and ron will have installed 2 panels. In thirty minutes 5 panels will have been placed. There are 12 panels that need to be placed so we know it will take another thirty minutes to place 5 more panels. After an hour only 10 panels will have been placed. So we need to add more time. There are only two panels that will need to be placed after an hour, so each group can place a panel. Tom and Ron will need 15 minutes so the answer is 60+15=75.
