Subtract 2 times x from 20, the difference is 7, find x.
20减x的2倍，差是7，求x．
<gadget id="calculator">20 - 7</gadget>
<output>13</output>

<gadget id="calculator">13 / 2</gadget>
<output>13/2 = around 6.5</output>

<result>13/2 = around 6.5</result>