When a=5, b=2; 2a-3b=how much.
当a=5，b=2；2a-3b=多少．
<gadget id="calculator">2 * 5</gadget>
<output>10</output>

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

<gadget id="calculator">10 - 6</gadget>
<output>4</output>

<result>4</result>