A store offers a new seasonal featured product. Let N be the random variable which designates the number of customers who come to the store during the season, where N Poi (20). It is estimated that the probability that a customer will buy this new product is 0,5 and this independently of one customer to another.

The store has a profit of 18$ for each unit sold. Each unsold unit should be stored for next year at the cost of 8$.

Determine the value of the number of units stored n that the store should have to maximize its average profit.