The number of students in a certain class is between 30-40, and the ratio of the number of boys to the number of girls is 3:4. How many boys are there in this class?
某班学生人数在30-40人之间，男生人数和女生人数的比是3：4，这个班的男生有多少人．
<gadget id="calculator">3 + 4</gadget>
<output>7</output>

<gadget id="calculator">4 / 7</gadget>
<output>4/7 = around 0.571429</output>

<gadget id="calculator">35 * (4/7)</gadget>
<output>20</output>

<result>20</result>