The time to produce the "N"th unit (T_N), for a given Learning Cure Rate (LCR), is equal to T_N= T_1 N^b where T1 is the time to produce the first unit and b is a factor for the LCR. If b = - 0.5 and the time to produce the first unit is 100 hours, what is the average time to produce the first three units?