When Xiaohu was doing a subtraction problem, he made a mistake of writing 9 for the 6 in the tens digit of the subtrahend, and a 6 for the 9 in the subtrahend ones digit. The final difference was 577. What should be the correct answer to this question?
小虎做一道减法题目时，把被减数十位上的6错写成了9，减数个位上的9错写成了6，最后所得的数差是577，这题的正确答案应该是多少？
<gadget id="calculator">90 - 60</gadget>
<output>30</output>

<gadget id="calculator">9 - 6</gadget>
<output>3</output>

<gadget id="calculator">30 + 3</gadget>
<output>33</output>

<gadget id="calculator">577 - 33</gadget>
<output>544</output>

<result>544</result>