Two identical small conducting balls B_1 and B_2 are given -7 pC and +4 pC charges respectively. They are brought in contact with a third identical…

Two identical small conducting balls $\displaystyle \mathrm{B}_{1}$ and $\displaystyle \mathrm{B}_{2}$ are given -$\displaystyle 7$ pC and +$\displaystyle 4$ pC charges respectively. They are brought in contact with a third identical ball $\displaystyle \mathrm{B}_{3}$ and then separated. If the final charge on each ball is -$\displaystyle 2$ pC , the initial charge on $\displaystyle \mathrm{B}_{3}$ was