The average score of Xiaohong's previous math tests was 85. This time, she needs 100 points to raise her average score to 88. How many times is this the first test?
小红前几次数学测验的平均成绩是85分，这一次要考100分，才能把平均成绩提高到88分，这一次是第几次测试？
<gadget id="calculator">100 - 85</gadget>
<output>15</output>

<gadget id="calculator">88 - 85</gadget>
<output>3</output>

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

<result>5</result>