There are several students in the classroom. After 10 girls leave, the number of boys is twice that of girls. After another 9 boys leave, the number of girls is 5 times that of boys. So how many girls were there in the first place?
教室里有若干学生，走了10名女生后，男生是女生人数的2倍，又走了9名男生后，女生是男生人数的5倍．那么最初有多少名女生．
<gadget id="calculator">5 * 9</gadget>
<output>45</output>

<gadget id="calculator">5 * 2</gadget>
<output>10</output>

<gadget id="calculator">10 - 1</gadget>
<output>9</output>

<gadget id="calculator">45 / 9</gadget>
<output>5</output>

<gadget id="calculator">5 + 10</gadget>
<output>15</output>

<result>15</result>