certain tourist spot sells two kinds of tickets, children's tickets and adult tickets. The price of children's tickets is 20 yuan, and the price of adult tickets is 40 yuan. If you are a group, you can also buy group tickets with an average of 30 yuan per person. A tourist group consisting of 9 families (each family consists of two adults, or two adults and one child) travels to the scenic spot. If they buy group tickets, they can spend 120 yuan less than if they buy individual tickets. , how many people are there in this tour group?
某旅游点有儿童票、成人票两种规格的门票卖，儿童票的价格为20元，成人票的价格为40元，如果是团体还可以买平均30元一位的团体票．一个由9个家庭组成的旅游团(每个家庭由两个大人，或两个大人、一个小孩组成)来景点旅游，如果他们买团体票，那么可以比他们各买各的票少花120元，则这个旅游团一共有多少人？
<gadget id="calculator">40 * 2 * 9</gadget>
<output>720</output>

<gadget id="calculator">30 * 2 * 9</gadget>
<output>540</output>

<gadget id="calculator">720 - 540 - 120</gadget>
<output>60</output>

<gadget id="calculator">30 - 20</gadget>
<output>10</output>

<gadget id="calculator">60 / 10</gadget>
<output>6</output>

<gadget id="calculator">3 * 6</gadget>
<output>18</output>

<gadget id="calculator">3 * 2</gadget>
<output>6</output>

<gadget id="calculator">18 + 6</gadget>
<output>24</output>

<result>24</result>