Managers at an automobile manufacturing plant would like to estimate

Managers at an automobile manufacturing plant would like to estimate the mean completion time of an assembly line operation, mu. The managers plan to choose a random sample of completion times and estimate mu via the sample. Assuming that the standard deviation of the population of completion times is 10.1 minutes, what is the minimum sample size needed for the managers to be 90% confident that their estimate is within 1.7 minutes of mu?

 Carry your intermediate computations to at least three decimal places. Write your answer as a whole number (and make sure that it is the minimum whole number that satisfies the requirements) (If necessary, consult a list of formulas)