There are 20 math competition questions. 5 points are awarded for each correct answer, and 2 points are deducted for each incorrect answer. Xiaoli scored 79 points, how many questions did she get right.
数学竞赛题共20道．每做对一题得5分，做错一题倒扣2分．小丽得了79分，她做对了多少道题．
<gadget id="calculator">5 * 20</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>