Consider the question. Sonny received 45 boxes of cookies from his friend yesterday. He gave 12 to his brother, 9 to his sister, and he gave 7 to his cousin. How many boxes of cookies were left for him?
 What is the step-by-step reasoning process to arrive at the answer: 17?
Sonny gave 12 + 9 + 7 = 28 boxes of cookies. Therefore, he was left with 45 - 28 = 17 boxes of cookies.