There are 72 students in the two classes of the fourth grade, including 35 girls, 36 students in Class 1, and 19 boys in Class 2, so how many girls are there in Class 1?
四年级的两个班共有学生72人，其中有女生35人，四1班有学生36人，四2班有男生19人，则四1班有女生多少人．
<gadget id="calculator">72 - 36 - 19</gadget>
<output>17</output>

<gadget id="calculator">35 - 17</gadget>
<output>18</output>

<result>18</result>