On Sunday, Xiao Huang’s family of eight visited the museum. The ticket price of the museum is 30 yuan per adult and 15 yuan per child. The total cost of buying tickets is 210 yuan. How many children are there?
星期日，小黄一家八口到博物馆参观，博物馆的票价是成人每人30元，儿童每人15元，买门票共花去210元钱，其中儿童有几人？
<gadget id="calculator">8 * 15</gadget>
<output>120</output>

<gadget id="calculator">210 - 120</gadget>
<output>90</output>

<gadget id="calculator">30 - 15</gadget>
<output>15</output>

<gadget id="calculator">90 / 15</gadget>
<output>6</output>

<gadget id="calculator">8 - 6</gadget>
<output>2</output>

<result>2</result>