could someone let me know what i'm doing wrong?

A study of the amount of time it takes a mechanic to rebuild the transmission for a 1992 Chevrolet Cavalier shows that the mean is 8.4 hours and the standard deviation is 1.8 hours. If 40 mechanics are randomly selected, find the probability that their mean rebuild time exceeds 8.1 hours.

mu (sample) = mu = 8.4

s.d. (sample) = 1.8/ sq. rt. 40

P( greater than 8.1) = (8.1-8.4)/(1.8/ sq. rt. 40)

i'm given a choice of four answers and this one definitely isn't one of them, ty.

A study of the amount of time it takes a mechanic to rebuild the transmission for a 1992 Chevrolet Cavalier shows that the mean is 8.4 hours and the standard deviation is 1.8 hours. If 40 mechanics are randomly selected, find the probability that their mean rebuild time exceeds 8.1 hours.

mu (sample) = mu = 8.4

s.d. (sample) = 1.8/ sq. rt. 40

P( greater than 8.1) = (8.1-8.4)/(1.8/ sq. rt. 40)

i'm given a choice of four answers and this one definitely isn't one of them, ty.

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