According to the law of charge conservation,
The net charge of the system before and after the decay should remain constant.
As the charge before the decay is +24e.
Thus, the net charge after the decay should be +24e.
Given that, the charge on 3 particles out of 12 is +2e each.
Thus, collective charge of the other 9 particles is,
[tex]\begin{gathered} q=Q-3(+2e) \\ q=24e-6e \\ q=+18e \end{gathered}[/tex]Thus, the collective charge on the other 9 particles is +18e.
