Xiao Ming answered 20 questions in the knowledge contest, 3 points for a correct answer, 2 points for a wrong answer, Xiao Ming finally got 45 points, how many questions did Xiao Ming answer correctly?
小明在知识竞赛中回答了20道题，答对一题得3分，答错一题扣2分，小明最后得了45分，小明答对了多少道题？
<gadget id="calculator">15 / 5</gadget>
<output>3</output>

<gadget id="calculator">20 - 3</gadget>
<output>17</output>

<result>17</result>