If A $20 \mathrm{~W}$ Laser Beam, Which Has an Initial Diameter Of

If a $20 \mathrm{~W}$ laser beam, which has an initial diameter of $2.0 \mathrm{~mm}$ , spreads out to a diameter of $2.0 \mathrm{~m}$ after traveling $10,000 \mathrm{~m}$ , what is the final intensity of the beam?

A) $20 \times 10^{-6} \mathrm{~W} / \mathrm{m}^{2}$
B) $6.4 \times 10^{-6} \mathrm{~W} / \mathrm{m}^{2}$
C) $20 \times 10^{-4} \mathrm{~W} / \mathrm{m}^{2}$
D) $20 \times 10^{-8} \mathrm{~W} / \mathrm{m}^{2}$
E) $6.4 \mathrm{~W} / \mathrm{m}^{2}$