Xiao Ming looks at his score sheet and predicts: If the next math test is 100 points, then the total average score is 91 points, if the next test is 80 points, then the total math score is 86 points, how many times has Xiao Ming’s math statistics table been take an exam.
小明看着自己的成绩表预测：如果下次数学考试100分，那么总平均分是91分，如果下次考80分，那么数学总平均成绩是86分，小明数学统计表是已经有多少次考试．
<gadget id="calculator">86 - 91 - 80</gadget>
<output>-85</output>

<gadget id="calculator">100 + (-85)</gadget>
<output>15</output>

<gadget id="calculator">91 - 86</gadget>
<output>5</output>

<gadget id="calculator">15 / 5</gadget>
<output>3</output>

<result>3</result>