Magnetics

A charged particle with charge $$q$$ enters a region of constant, uniform and mutually orthogonal fields $$\overrightarrow E$$ and $$\overrightarrow B$$ with a velocity $$\overrightarrow v$$ perpendicular to both $$\overrightarrow E$$ and $$\overrightarrow B,$$ and comes out without any change in magnitude or direction of $$\overrightarrow v$$. Then