Wang Liang participated in a mathematics competition. He got 4 points for each correct answer, 1 point for each wrong answer, and no point for no answer. It is known that he answered all 25 questions in the test paper and scored 80 points in total. How many questions did Wang Liang answer correctly?
王亮参加一次数学竞赛，每答对一道题得4分，打错一道题扣1分，不答不得分也不扣分．已知试卷中的25道题他都答了，共得了80分，王亮答对了几道题？
<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>