Students participate in extracurricular activities. There are 4 groups of rope skippers and 4 groups of table tennis players. Each group of rope skippers has 12 people, and each group of table tennis players has 9 people. How many students are there in total?
同学们参加课外活动，跳绳的和打乒乓球的各有4组，跳绳的每组有12人，打乒乓球的每组有9人，参加课外活动的同学一共有多少人？
<gadget id="calculator">12 + 9</gadget>
<output>21</output>

<gadget id="calculator">21 * 4</gadget>
<output>84</output>

<result>84</result>