Yang Yang wrote 7 numbers, the average of the first four numbers is 20, and the average of the last three numbers is 13, so what is the average of the 7 numbers written by Yang Yang?
杨杨写了7个数，前四个数的平均值为20，后三个数的平均值为13，那么杨杨写出的7个数的平均值是多少．
<gadget id="calculator">4 * 20</gadget>
<output>80</output>

<gadget id="calculator">3 * 13</gadget>
<output>39</output>

<gadget id="calculator">80 + 39</gadget>
<output>119</output>

<gadget id="calculator">119 / 7</gadget>
<output>17</output>

<result>17</result>