2:10:16 ratio simpification (I know the answer, but i need the working)

Question 5 spring semester final exam math evaluate

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?

Write the equation for the parabola that has x− intercepts (−2,0) and (4,0) and y− intercept (0,4).