Suppose that the number of customers entering a department store in a day is a random variable with mean of 50 customers/day. Suppose that the amounts of money spent by each one of these customers are statistically independent random variables with mean $8 (per customer). Also assume that the amount of money spent by each customer is independent of the number of customers to enter the store. Calculate the expected amount of money spent by the customers that enter the store during a single day.