If a=3, b=4, c=5, then how much is a+2b-c=.
如果a=3，b=4，c=5，那么a+2b-c=多少．
<gadget id="calculator">2 * 4</gadget>
<output>8</output>

<gadget id="calculator">8 - 5</gadget>
<output>3</output>

<gadget id="calculator">3 + 3</gadget>
<output>6</output>

<result>6</result>