There are only two questions in a math test. As a result, there are 12 people in the class who are all correct, 27 people get one question right, 21 people get the second question wrong, and how many people get both questions wrong.
一个数学检测只有两道题，结果全班有12人全对，有一题有27人做对，第二道题有21人做错，两道题都做错的有多少人．
<gadget id="calculator">27 - 12</gadget>
<output>15</output>

<gadget id="calculator">21 - 15</gadget>
<output>6</output>

<result>6</result>