When x+1=4, then 2x+1=how much.
当x+1=4，那么2x+1=多少．
<gadget id="calculator">4 - 1</gadget>
<output>3</output>

<gadget id="calculator">2 * 3</gadget>
<output>6</output>

<gadget id="calculator">6 + 1</gadget>
<output>7</output>

<result>7</result>