The teacher distributed a bunch of apples to the children, and each of them distributed the same amount. If the apples are distributed to 9 people, there are 21 apples left; if the apples are distributed to 12 people, there are only 12 apples left. Question: How many apples are there in total?
老师把一堆苹果分给小朋友，每人分的同样多．如果分给9个人，那么还剩下21个苹果；如果分给12个人，就只剩下12个苹果．请问：这堆苹果一共有多少个？
<gadget id="calculator">21 - 12</gadget>
<output>9</output>

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

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

<gadget id="calculator">3 * 9</gadget>
<output>27</output>

<gadget id="calculator">27 + 21</gadget>
<output>48</output>

<result>48</result>