We have,
[tex]a:b=3:6,a+b=96[/tex]
Introduce variable [tex]x[/tex] such that [tex]a=3x,b=6x[/tex]
The sum [tex]a+b=96[/tex] is therefore [tex]9x=96\implies x=10.\overline{6}[/tex]
So,
[tex]a=3\cdot10.\overline{6}=\boxed{32}[/tex] (sadia's age)
[tex]b=6\cdot10.\overline{6}=\boxed{64}[/tex] (father's age)
Hope this helps :)
