There are 12 people from Class 6 and 2 to participate in the tree planting activity. Each of the girls planted 2 trees, and each of the boys planted 3 trees. A total of 33 trees were planted. How many boys are there?
六二班有12人参加植树活动．女生每人栽了2棵树，男生每人栽了3棵树，一共栽了33棵树．男生有多少人．
<gadget id="calculator">12 * 3</gadget>
<output>36</output>

<gadget id="calculator">36 - 33</gadget>
<output>3</output>

<gadget id="calculator">3 - 2</gadget>
<output>1</output>

<gadget id="calculator">3 / 1</gadget>
<output>3</output>

<gadget id="calculator">12 - 3</gadget>
<output>9</output>

<result>9</result>