Which equation can be used to solve the problem? Explain why also please!

Rockwell hardness of pins of a certain type is known to have a mean value of 50 and a standard deviation of 1.1. (round your answers to four decimal places.) (a) if the distribution is normal, what is the probability that the sample mean hardness for a random sample of 8 pins is at least 51?

Richard save $32 in march he saved $48 in april and $38 in may then richard spent $113 on a keyboard how much money does richard have left

The holiday party will cost $160 if 8 people attend.if there are 40 people who attend the party, how much will the holiday party cost