In the following formula, how much is equal to the result of 50*2-80.
下面的算式中，多少与50*2-80的结果相等．
<gadget id="calculator">50 * 2</gadget>
<output>100</output>

<gadget id="calculator">100 - 80</gadget>
<output>20</output>

<result>20</result>