The number density of free electrons in a copper conductor is  $8.5\times {10}^{28}/{\mathrm{m}}^3$ . The area of the wire is $2\times {10}^{-6}{\mathrm{m}}^2$  and it carry a current of 3A. The time taken by an electron to drift from one end of a wire 3 m long to its other end is _____$\times {10}^3\sec .$