Let us suppose that charge on both spheres is, $q$ and when it touches with the uncharged sphere then charge distributed in order of $\frac{q}{2}$ each $A \& B$,

Before-

$F=K\frac{q^2}{r^2}=4\times {10}^{-5} \mathrm{N}$

after-

$$\begin{gathered} F_{AC}=K\frac{{{\displaystyle \frac{q}{4}}}^2}{{{\displaystyle \frac{r}{4}}}^2}=K\frac{q^2}{r^2} \& F_{BC}=K\frac{{\displaystyle \frac{q^2}{2}}}{{\frac{r}{4}}^2}=K\frac{2q^2}{r^2} \\ {F}_C=F_{BC}-F_{AC}=K\frac{q^2}{r^2} =4\times {10}^{-5} \mathrm{N} \end{gathered}$$

From $C$ to $A$