The Boundary Shown Is That of a Uniform Magnetic Field

Multiple Choice

The boundary shown is that of a uniform magnetic field directed in the positive z direction.An electron enters the magnetic field with a velocity pointing along the x axis and exits 0.63 μs later at point A.What is the magnitude of the magnetic field?

A) 18 μT
B) 14 μT
C) 28 μT
D) 34 μT
E) 227 μT