The little sloppy mistakenly regarded the second addend 309 in an addition problem as 390, and the result was 850. What is the correct sum?
小马虎不认真把一道加法题目的第二个加数309看成了390，结果算出来是850，正确的和应是多少．
<gadget id="calculator">850 - 390</gadget>
<output>460</output>

<gadget id="calculator">460 + 309</gadget>
<output>769</output>

<result>769</result>