1/8 divided by 1\2 divide write in simplest form. check by multiplication

Iam so stuck. what is the worked out answer for this question?

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?

What is the missing step in this proof ?