If 2x+8=13, then 8x-13.5=how much.
如果2x+8=13，那么8x-13.5=多少．
<gadget id="calculator">13 - 8</gadget>
<output>5</output>

<gadget id="calculator">5 / 2</gadget>
<output>5/2 = around 2.5</output>

<gadget id="calculator">8 * (5/2)</gadget>
<output>20</output>

<gadget id="calculator">20 - 13.5</gadget>
<output>6.5</output>

<result>6.5</result>