In a certain manual operation, the first work unit required $5\mathrm{.}49$min to complete and the learning rate is

known to be $84\%$ in the Crawford model. Using this learning curve model, determine the average cumulabive

times to produce $($a$)$ the second unit, $($b$)$ the ${10}^o$ unit, and $($c$)$ the ${100}^P$ unit.