The clean-up crew of medium-sized firm has an average clean-up time of 72.0 total hours with variance of 64 hours squared. The clean-up times are bell-shaped.
(a) What proportion of time will it take the clean-up crew 56 or more hours for cleaning the plant?
(b) Ninety-five percent of the time total clean-up time will fall in what interval about the mean?
State the lower and upper limits of interval.