Two charged particles, having same kinetic energy, are allowed to...

Radius of charged particle moving in circular path $R = \dfrac{\sqrt{2mK}}{qB}$, here, $B$ is magnetic field and $K$ is kinetic energy.

So, $q = \dfrac{\sqrt{2mK}}{RB}$

Now, ratio of the charges is $\dfrac{{q}_{1}}{{q}_{2}} = \sqrt{\dfrac{{m}_{1}}{{m}_{2}}} \times \dfrac{{R}_{2}}{{R}_{1}} = \sqrt{\dfrac{9}{4}} \times \dfrac{5}{6} = \dfrac{5}{4}$