A parallel plate capacitor constructed of two disks spaced 2.0 mm apart and is charged to a potential difference of 500V. An ion with a charge of +2e and four times the mass of proton is shot through a small hole in the negative plate with a speed of 2x10^5 m/s. What is the farthest distance from the negative plate that the ion reaches? I know that the answer here is 1.67 mm, but I don't know how to solve for it. Can anyone show me?