There are some students reading in the library, the number of boys is girls (7/8), and then the girls left (1/4), 4 boys left, and the remaining number of boys and girls is equal. How many boys are there?
图书馆有一些学生在看书，其中男生人数是女生的(7/8)，后来女生走了(1/4)，男生走了4人，剩下的男、女生人数相等．求原来男生有多少人？
<gadget id="calculator">7 / 8</gadget>
<output>7/8 = around 0.875</output>

<gadget id="calculator">4 * (7/8)</gadget>
<output>7/2 = around 3.5</output>

<gadget id="calculator">1 / 4</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">(7/8) - 1</gadget>
<output>-1/8 = around -0.125</output>

<gadget id="calculator">(1/4) + (-1/8)</gadget>
<output>1/8 = around 0.125</output>

<gadget id="calculator">(7/2) / (1/8)</gadget>
<output>28</output>

<result>28</result>