From the question;
The ratio of boys to girls is
[tex]\begin{gathered} Girls\text{ : Boys} \\ 3\text{ : 4} \end{gathered}[/tex]Increasing the ratio
[tex]\begin{gathered} 3\text{ : 4 = 3}\times9\colon4\times9\text{ } \\ \text{ = 27 : 36} \end{gathered}[/tex]So therefore,
The possible number of the girls is 27 and the possible number of the boys is 36