Lower and upper limits of the interval using Empirical Rule.

The clean-up crew of a medium-sized firm has an average clean-up time of 72.0 total hours with a variance of 64 hours squared. The clean-up times are bell-shaped.

(a) What proportion of the time will it take the clean-up crew 56 or more hours for cleaning the plant?

(b) Ninety-five percent of time the total clean-up time will fall within what interval about the mean?
Status the lower and upper limits of the interval.