Teddy will buy at least 15 bags of ice for the graduation picnic. Each large bag of ice costs $4.00, and each small bag of ice costs $2.50. He will spend up to $50 on ice. Write an equation to see how many bags of ice he can buy?

9 large, 6 small

2 large, 11 small

10 large, 5 small

6 large, 10 small