(12/(x+3))=2.5.
(12/(x+3))=2.5．
<gadget id="calculator">2.5 * 3</gadget>
<output>7.5</output>

<gadget id="calculator">12 - 7.5</gadget>
<output>4.5</output>

<gadget id="calculator">4.5 / 2.5</gadget>
<output>1.8</output>

<result>1.8</result>