Study amount of time a mechanic to rebuild a transmission

Question

A study of the amount of time it takes to rebuild the transmission for a 1992 Chevrolet Cavalier shows that the mean is 9.1 hours and the standard deviation is 1.8 hours. If 75 mechanics are randomly selected, find the probability that their mean build time is more than 9.2 hours

Answer 1

P(M_xbar>9.2) = P(Z>((9.2-9.1)/(1.8/sqrt(75)) = P(Z>0.48) = Normalcdf(0.48, 1000, 0, 1) = 0.3156

or

Normalcdf(9.2, 1000, 9.1, (1.8/sqrt(75))) = 0.3156