The time (in minutes) that a worker takes to perform a certain task is a time with Normal distribution.

It is known that the probability that the operator takes more than 13 minutes is 0.0668 and that it takes less

minutes and 0.1587.

(a) Calculate the average time required to perform the task and the respective standard deviation.

(b) Calculate the probability that the operator will take between 9 and 12 minutes to execute it