A small supermarket is trying to determine how many copies of PEOPLE magazine

A small supermarket is trying to determine how many copies of PEOPLE magazine it should order next week. The owner believes the demand for PEOPLE is governed by the following discrete random variable:             
             
Demand Probability            
15 0.1            
20 0.2            
25 0.3            
30 0.25            
35 0.15            
             
The Supermarket pays $1.00 for each copy of PEOPLE and sells it for $1.95. Each unsold copy can be returned for $.50. How many copies of PEOPLE should the store order?