Add parentheses to the formula 840-240+60, change the order of operations, and get the number.
在算式840-240+60中添上括号，改变运算顺序，得数是多少．
<gadget id="calculator">840 - 240</gadget>
<output>600</output>

<gadget id="calculator">600 + 60</gadget>
<output>660</output>

<result>660</result>