Let us assume that the initial charges on the spheres were $Q_1$ and $Q_2$ respectively and the final charges on the spheres are $q_1$ and $q_2$. Finally the potential of both the spheres is the same.

$\frac{k{q}_1}{R_1}=\frac{k{q}_2}{R_2}$

$\Rightarrow q_2=q_1\frac{R_2}{R_1}$

$q_1+q_2=Q_1+Q_2$

$q_1=\frac{R_1}{R_1+R_2}\left(Q_1+Q_2\right)$

$\Rightarrow q_1=\frac{10}{10+20}\left(0.5+0.7\right)=0.4 \mathrm{\mu C}$

$q_2=\frac{R_2}{R_1+R_2}\left(Q_1+Q_2\right)$

$\Rightarrow q_2=\frac{20}{10+20}\left(0.5+0.7\right)=0.8 \mathrm{\mu C}$