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

v $= \frac{E×B}{B^2}$

As v of charged particle is remaining constant, it means force acting on charged particle is zero.

So,   q(v × B) = qE

⇒    v × B = E

⇒   v $= \frac{E×B}{B^2}$