You have a plate capacitor which is grounded on the bottom and is held at a potential V which is then set to 0. You are given the length of the plates and the distances between them. A test charge is brought in with the charge and mass given along with its velocity. For a vanishing magnetic field the test charge just moves to the right on a straight line and escapes the capacitor. If you increase the magenetic field the trajectory will bend. The problem is to find the largest magnetic field (increasing the value from 0) such that the test still escapes the capacitor without crashing into the plates. I am totally clue less on this problem but I think perhaps you must do soem geometry with the radius, the length of the plates and the distances between them and maybe some how incorporate the fact the qvB = qE (and balance that equation) ? But this is all I have been able to come up with, any help would be greatly appreciated!