Motion in One Dimension

An electron with initial velocity $v_{x}_{o} = 1.0 \times 10^{4}$ meters/sec enters a region where it is electrically accelerated. It emerges with a velocity $v_{x} = 4.0 \times 10^{6}$ meters/sec. What was its acceleration, assumed constant? The accelerated region is 1 cm. So acceleration is defined as $\frac{\Delta v}{\Delta t}$. How would I use the fact that the accelerated region is 1 cm long?

Thanks