Ben needs to buy an equal number of sunglasses and beach balls to place in gift bags. Each pair of sunglasses costs $4 and each beach ball costs $2.50. If he has $45 to spend on the sunglasses and beach balls, then the inequality 4x + 2.5x greater than or equal to 45 can be used to find the number of each item he can buy. How much money will he have left after buying the greatest number of sunglasses and beach balls?