6. (10 Marks) Zack Pop has been a produce plant production manager for the last 10 years. One produce item, zucchini, is sold in cases, with daily sales averaging 400 cases. Daily sales are also assumed to be normally distributed. Furthermore, 85% of the time sales are between 350 and 450 cases. Each case is purchased for $10 wholesale and sells for 515 retail. All cases that are not sold must be discarded. a. Estimate the standard deviation of the sales distribution. b. Using the standard deviation found in part a, determine how many cases of zucchini that Zach should stock