When the little sloppy calculated an addition problem, he regarded the "3" in the tens place as "5", and the result was 784. What should be the correct answer.
小马虎在计算一道加法题时，把十位上的"3"看成了"5"，结果是784．正确的答案应是多少．
<gadget id="calculator">50 - 30</gadget>
<output>20</output>

<gadget id="calculator">784 - 20</gadget>
<output>764</output>

<result>764</result>