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?
Sonny gave 12 + 9 + 7 = 
<gadget id="calculator">12+9+7</gadget>
<output>28</output>
28 boxes of cookies.
Therefore, he was left with 45 - 28 = 
<gadget id="calculator">45-28</gadget>
<output>17</output>
17 boxes of cookies.

<result>17</result>