In a certain mathematics competition, 5 points are awarded for a correct answer, and 2 points are deducted for a wrong or missed answer. There are 20 questions in total. Xiaosi finally scored 79 points.
某次数学竞赛，做对一题得5分，做错或没做扣2分，一共有20题，小丝最后得了79分，小丝答对了多少题．
<gadget id="calculator">20 * 5</gadget>
<output>100</output>

<gadget id="calculator">100 - 79</gadget>
<output>21</output>

<gadget id="calculator">5 + 2</gadget>
<output>7</output>

<gadget id="calculator">21 / 7</gadget>
<output>3</output>

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

<result>17</result>