A copper sphere of diameter 18 cm is drawn into a wire of diameter 4 mm.

We have,

Radius of the sphere, $R=\frac{18}{2}=9 \mathrm{~cm}$ and

Radius of the wire, $r=\frac{4}{2}=2 \mathrm{~mm}=0.2 \mathrm{~cm}$

Let the length of the wire be $l$.

Now,

Volume of the wire $=$ Volume of the copper sphere

$\Rightarrow \pi r^{2} l=\frac{4}{3} \pi R^{3}$

$\Rightarrow l=\frac{4 R^{3}}{3 r^{2}}$

$\Rightarrow l=\frac{4 \times 9 \times 9 \times 9}{3 \times 0.2 \times 0.2}$

$\therefore l=24300 \mathrm{~cm}=243 \mathrm{~m}$

So, the length of the wire is 243 m.