Solve the equation and check: 5x-2x=12.
解方程并检验：5x-2x=12．
<gadget id="calculator">5 * 4</gadget>
<output>20</output>

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

<gadget id="calculator">20 - 8</gadget>
<output>12</output>

<gadget id="calculator">5 - 2</gadget>
<output>3</output>

<gadget id="calculator">12 / 3</gadget>
<output>4</output>

<result>4</result>