Add parentheses to the formula below, and ask for multiplication in the last step: what is the result of 560-280*3.
给下边的算式添上括号，要求最后一步算乘法：560-280*3结果是多少．
<gadget id="calculator">560 - 280</gadget>
<output>280</output>

<gadget id="calculator">280 * 3</gadget>
<output>840</output>

<result>840</result>