the newsvendor ratio of a newsvendor problem is 0.8 and the demand distribution is normally distributed with mean 10 and variance 4, Recall that the random variable for demand was denoted as D. Let Z be a random variable following standard normal distribution N(0,1). Write a proper value of x and y in the following equation: P(D q) = P(Z (q-x)/y) (a) What is the value of x? (b) What is the value of y? (c) What is an approximate value of z such that Pr (Z z) = 0.8? (Use z table) (d) What is the optimal ordering quantity in this case? Round your answer to the closest integer.