Among the students who signed up for the mathematics competition in the school, the number of students in the fifth grade was in the sixth grade (5/6), and 2 people were added later. At this time, the ratio of the number of students in the fifth grade to the sixth grade was 9:10. How many people in the sixth grade signed up? Entering a math competition?
学校报名参加数学竞赛的学生中，五年级人数是六年级的(5/6)，后来又补报了2人，这时五年级与六年级人数的比是9：10，六年级有多少人报名参加数学竞赛？
<gadget id="calculator">9 / 10</gadget>
<output>9/10 = around 0.9</output>

<gadget id="calculator">5 / 6</gadget>
<output>5/6 = around 0.833333</output>

<gadget id="calculator">(9/10) - (5/6)</gadget>
<output>1/15 = around 0.066667</output>

<gadget id="calculator">2 / (1/15)</gadget>
<output>30</output>

<result>30</result>