15 machines work at the same rate. Together, the 15 machines can complete an order in 8 hours. 3 of the machines break down after working for 6 hours. The other machines carry on working until the order is complete. In total, how many hours does EACH

The total number of 'machine hours' needed to complete an order is (15x8) = 120 hoursThe total number of hours worked by the broken machines = (6x3) = 18 hoursTherefore the total number of machine hours needed from the other 12 machines to complete the order = (120-18) = 102Per machine the total number of working hours therefore equals (102/12) = 8.5 hours