What is the probability that a random sample of n=45 oil changes is a sample mean less than 20 minutes? the mean is 21.1, standard deviation is 4.6

Pyotr tchaikovsky sporting goods operates on a 45% overhead based on the selling price, which results in an overhead of $65.34 on the newest version of an air hockey game set. if the air hockey game set costs pyotr tchaikovsky sports $49.32, find the selling price, the markup, and the net profit.