When a=4, b=5, c=6, what is the value of ab-c
当a=4，b=5，c=6时，ab-c的值是多少
<gadget id="calculator">4 * 5</gadget>
<output>20</output>

<gadget id="calculator">20 - 6</gadget>
<output>14</output>

<result>14</result>