Big Pharma is currently selling a migraine medication called…

Big Pharma is currently selling a migraine medication called Go Away, Migraine. Suppose that this product works for 80% of all people who use it.   Suppose you choose one random sample of 350 people from the population of people who buy the product. The sample proportion of people for whom the product worked is 0.75. Determine the z-score for this sample proportion.