If 15-x=6.5, then 2x-5=how much.
如果15-x=6.5，那么2x-5=多少．
<gadget id="calculator">15 - 6.5</gadget>
<output>8.5</output>

<gadget id="calculator">2 * 8.5</gadget>
<output>17</output>

<gadget id="calculator">17 - 5</gadget>
<output>12</output>

<result>12</result>