There are 20 math problems in the math competition. It is stipulated that 5 points will be awarded for a correct one, and 2 points will be deducted for a wrong one. Xiaofang scored 79 points. How many problems did she get wrong?
数学竞赛共20道数学题，规定：对一道给5分，错一道倒扣2分，小芳得了79分，她做错了几道？
<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>

<result>3</result>