The four numbers are 7, 8, 12, 13 respectively, what is their average
四个数分别是7、8、12、13，它们的平均数是多少
<gadget id="calculator">7 + 8 + 12 + 13</gadget>
<output>40</output>

<gadget id="calculator">40 / 4</gadget>
<output>10</output>

<result>10</result>