Fifty percent of the customers who go to Sears Auto Center for tires buy four tires and

Question:

Fifty percent of the customers who go to Sears Auto Center for tires buy four tires and 30% buy two tires. Moreover, 18% buy fewer than two tires, with 5% buying none.
a. Find the expected value and the standard deviation of the number of tires a customer buys.
b. If Sears Auto Center makes a $15 profit on every tire it sells, what is its expected profit if it services 120 customers?