A perishable dairy product is ordered daily at a particular supermarket. The product costs $1.19 per unit and sells for $1.65. If units are unsold at the end of the day, the supplier takes them back at a refund of $1.

(a) Assume that daily demand is normally distributed with mean 150 and standard deviation 30. What is your recommended daily order quantity for the supermarket? 

(b) What is the probability that supermarket will sell all the units it orders?

 (c) The Supermarket's supplier wants to deliver an even 160 units per order so that it can fit other items in the cooler bins in the delivery truck. What is the refund amount it needs to give to the Supermarket so that it will order 160 units?