i have prob in which 8charges of different magnitude are placed at the corners of a cube of length = 1m.my ques is hw to find the force excerted by any 7 charges on the 8th charge.

The Force Exerted on the 8th charge will be the sum of all the forces exerting on it

individually fid the force exerted by each charge on that 8th carge and add them up vectorially like in newtons 2nd law of motion