Mr. Hu gave 25 questions, and it was stipulated that 4 points would be given for each correct answer, and 1 point would be deducted for each wrong answer. Xiaoxia got 80 points.
胡老师出了25道题，规定做对一题给4分，不做或做错一题倒扣1分，小侠得了80分，他做对了多少道题．
<gadget id="calculator">25 * 4</gadget>
<output>100</output>

<gadget id="calculator">100 - 80</gadget>
<output>20</output>

<gadget id="calculator">4 + 1</gadget>
<output>5</output>

<gadget id="calculator">20 / 5</gadget>
<output>4</output>

<gadget id="calculator">25 - 4</gadget>
<output>21</output>

<result>21</result>