Let a be the number of soups ordered and b be the number of sandwiches ordered. We know that, a + b = 18, so a = 18 - b. Now we form an equation for the total cost, which is: 4.5a + 7.75b = 113.5. Now, we substitute the value of a into the cost equation to form a single equation in terms of b, number of sandwiches, only. 4.5(18 - b) + 7.75b = 113.5. Solving for b, we get b = 10. Therefore, the answer is D.
