There are 50 students in the class, each of whom has exactly one kind of settable or ruler, 28 have rulers, among those who have settables, 14 are boys, if it is known that there are 31 girls in the class, then there are 31 girls How many girls are there in .
全班50个学生，每人恰有三角板或直尺中的一种，28人有直尺，有三角板的人中，男生是14人，若已知全班共有女生31人，那么有直尺的女生有多少人．
<gadget id="calculator">50 - 28 - 14</gadget>
<output>8</output>

<gadget id="calculator">31 - 8</gadget>
<output>23</output>

<result>23</result>