At most, Keith can spend $90 on sandwiches and chips for a company lunch. He already bought chips for $15 and will buy sandwiches that cost $6 each. The inequality 15 + 6s ≤ 90 represents the described cost, where s is the maximum number of sandwiches that could be bought. What is the maximum number of sandwiches Keith can buy? A) 12 sandwiches B) 13 sandwiches C) 17 sandwiches D) 18 sandwiches