Students participate in extracurricular activities. There are 3 groups of rope skippers and 3 groups of table tennis players. Each group of rope skippers has 18 people, and each group of table tennis players has 12 people. How many people participated in the activity?
同学们参加课外活动．跳绳的和打乒乓球的各有3组，跳绳的每组18人，打乒乓球的每组12人，一共有多少人参加活动？
<gadget id="calculator">18 + 12</gadget>
<output>30</output>

<gadget id="calculator">30 * 3</gadget>
<output>90</output>

<result>90</result>