The math test paper has 20 questions. 7 points for a correct answer; 4 points for a wrong answer; 0 points for no answer. Zhang Hong scored 100 points, how many questions did she not answer?
数学测试卷有20道题．做对一道得7分；做错一道扣4分；不答得0分．张红得了100分，她有多少道题没答．
<gadget id="calculator">20 - 16 - 3</gadget>
<output>1</output>

<result>1</result>