What Electric Field is Needed to Undeflect Electrons in a Magnetic Field?

[Stryker321]

A beam of electrons is accelerated through a potential difference of 11kV before entering a velocity selector. If the B-field of the velocity selector is perpendicular to the velocity and has a value of 0.05 T, what value of the E-field is required (in the magnetic field region) if the particles are to be undeflected?

What I know:
F = qvB
and
F = qE

Therefore E = vB

But how on Earth do I find the velocity? Please help!

 

[nasu]

But how on Earth do I find the velocity? Please help!

Read this again:
"A beam of electrons is accelerated through a potential difference of 11kV"
What energy will the electrons have?