Relaxation time, drift speed, and current

A metal conductor with a square cross-section of side, $l$‍, carries a current, $I=3.6\text{A}$‍.

The metal has ${10}^{30}$‍ free electrons per ${\text{m}}^3$‍ drifting slowly at ${10}^{-5}{\displaystyle \frac{\text{m}}{\text{s}}}$‍.