Need help please and thank you

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?

Given the two similar triangles, how do i find the missing length? if a=4, b=5, and b'=7.5 find a'

What is the circumference of a circle with an area of 50.24 cm²?