There are 45 students in class 31, which are divided into 5 extracurricular activity groups on average. There are exactly two groups for girls. How many girls are there?
三1班有45人，平均分成5个课外活动小组，女生刚好二个小组，女生有多少人？
<gadget id="calculator">45 / 5</gadget>
<output>9</output>

<gadget id="calculator">9 * 2</gadget>
<output>18</output>

<result>18</result>