The ratio of male to female students in Class 61 is 5:4. This semester, 4 boys will be transferred and 4 girls will be transferred in. The ratio of male to female students will be 7:8. How many boys are there in Class 61?
六一班男女生的人数比为5：4，这学期转走4名男生，转入4名女生，男女生的人数比变为7：8，请问原来六一班有多少男生？
<gadget id="calculator">5 + 4</gadget>
<output>9</output>

<gadget id="calculator">5 / 9</gadget>
<output>5/9 = around 0.555556</output>

<gadget id="calculator">7 + 8</gadget>
<output>15</output>

<gadget id="calculator">7 / 15</gadget>
<output>7/15 = around 0.466667</output>

<gadget id="calculator">(5/9) - (7/15)</gadget>
<output>4/45 = around 0.088889</output>

<gadget id="calculator">4 / (4/45)</gadget>
<output>45</output>

<gadget id="calculator">45 * (5/9)</gadget>
<output>25</output>

<result>25</result>