A set of data 22, 15, 8, the average of a is 12, then a = how much.
一组数据22，15，8，a的平均数是12，那么a=多少．
<gadget id="calculator">12 * 4</gadget>
<output>48</output>

<gadget id="calculator">48 - 22 - 15 - 8</gadget>
<output>3</output>

<result>3</result>