In a certain mathematics competition, there are two ways to give points. One is to give 5 points for a correct answer, 2 points for no answer, and no points for a wrong answer; the other is to give 40 points first, and 3 points for a correct answer. No points will be given for no answer, 1 point will be deducted for wrong answer. An examinee scored 81 points in both scoring methods. How many questions are there in this competition?
某次数学比赛，分两种方法给分，一种是答对一题给5分，不答给2分，答错不给分；另一种是先给40分，答对一题给3分，不答不给分，答错扣l分．某考生两种判分方法均得81分，这次比赛共有多少题．
<gadget id="calculator">15 * 3</gadget>
<output>45</output>

<gadget id="calculator">45 - 81</gadget>
<output>-36</output>

<gadget id="calculator">40 + (-36)</gadget>
<output>4</output>

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

<gadget id="calculator">15 + 3 + 4</gadget>
<output>22</output>

<result>22</result>