$B=2 \times 10^{-4} \,\mathrm{Wb} \mathrm{m}^{-2}=2 \times 10^{-4} \,\mathrm{T}$

$\mathrm{R}=6\, \mathrm{cm}=6 \times 10^{-2} \,\mathrm{m}$

$\mathrm{As}, \mathrm{Bqv}=\frac{\mathrm{mv}^{2}}{\mathrm{R}}$ or $\frac{\mathrm{q}}{\mathrm{m}}=\frac{\mathrm{v}}{\mathrm{BR}}$

Substituting the given values, we get;

$\frac{\mathrm{q}}{\mathrm{m}}=\frac{3 \times 10^{6}}{2 \times 10^{-4} \times 6 \times 10^{-2}}=2.5 \times 10^{11}\, \mathrm{C} / \mathrm{kg}$