Please explain me with proper explanation.

2. An ion milling machine uses a beam of gallium ions (m = 70u) to carve microstructures from a target. A region of uniform electric field between parallel sheets of charge is used for precise control of the beam direction. Single ionized gallium atoms with initially horizontal velocity of 1.8 x 104 m/s enter a 2.0 cm-long region of uniform electric field which points vertically upward, as shown in Fig. 2. The ions are redirected by the field, and exit the region at the angle 0 shown. If the field is set to a value of E = 90 N/C, what is the exit angle 0