Xiaoxiao did an addition problem. He regarded the second addend 420 as 240, and the result was 390. What is the correct result?
小小做一道加法题，他把第二个加数420看成了240，结果算出和是390，正确的结果是多少．
<gadget id="calculator">390 - 240</gadget>
<output>150</output>

<gadget id="calculator">150 + 420</gadget>
<output>570</output>

<result>570</result>