There are 52 students in the whole class of Class 1, of which male students accounted for (7/13), and the students in this class (3/4) participated in the "Red Ribbon" promotional activity. At least how many male students in Class 1 participated in the "Red Ribbon" promotional activities.
六1班全班有52名同学，其中男同学占(7/13)，这个班(3/4)的同学参加了"红丝带"宣传活动．六1班参加"红丝带"宣传活动的男同学至少有多少人．
<gadget id="calculator">3 / 4</gadget>
<output>3/4 = around 0.75</output>

<gadget id="calculator">7 / 13</gadget>
<output>7/13 = around 0.538462</output>

<gadget id="calculator">52 * (3/4) * (7/13)</gadget>
<output>21</output>

<result>21</result>