Use "*" to represent a new operation, which is defined as follows: A*B=A*B-(A+B), then 3*6=how much.
用"*"表示一种新运算，它是这样定义的：A*B=A*B-(A+B)，则3*6=多少．
<gadget id="calculator">3 * 6</gadget>
<output>18</output>

<gadget id="calculator">3 + 6</gadget>
<output>9</output>

<gadget id="calculator">18 - 9</gadget>
<output>9</output>

<result>9</result>