In a certain mathematics competition, there were 20 questions in total, 5 points were awarded for each correct answer, 2 points were deducted for failure or error, Xiao Cong scored 79 points, how many questions did he get right?
某次数学竞赛，共有20道题，每道题做对得5分，没做或做错都要扣2分，小聪得了79分，他做对了多少道题．
<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>