It is known that 2x+5=13, so how much is 7x-13=.
已知2x+5=13，那么7x-13=多少．
<gadget id="calculator">13 - 5</gadget>
<output>8</output>

<gadget id="calculator">8 / 2</gadget>
<output>4</output>

<gadget id="calculator">7 * 4</gadget>
<output>28</output>

<gadget id="calculator">28 - 13</gadget>
<output>15</output>

<result>15</result>