Please help me I really don't understand and no one will help me because of these absurd answers

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 multiplys to be 1 but adds up to be 4

How is this equation completed? i cannot find any examples in the book.