MODULE E LEARNING CURVES 81 c. To find the time for units 12 through 15, we take the total cumulative time for units I to 15 and subtract the total time for units I to 11, which was computed in part (b). Total time for the first 15 units = (56 hours)(8.511) = 476.6 hours. So the time for units 12 through 15 is 476.6 - 379.5 = 97.1 hours. (This figure could also be confirmed by computing the times for units 12, 13, 14, and 15 separately using the unit-time coefficient column and then adding them.) Expected cost for units 12 through 15 = (97.1 hours) ($30 per hour) = $2,913