Posted by ike on .
6. A charged particle remains stationary in an upwardly directed E field between two parallel charged plates separated by 2 cm. Compute the potential difference V between
the plates if the particle has a mass of 4 x 1013 kg and a charge of +2.4 x 1018 C.

physics 
drwls,
M g = Q E = Q V/d
where d is the plate separation and Q is the charge.
Solve for d. You know all the other terms