A 10-W laser emits a beam of light 4.0 mm in diameter. The laser is aimed at

Question:

A 10-W laser emits a beam of light 4.0 mm in diameter. The laser is aimed at the Moon. By the time it reaches the Moon, the beam has spread out to a diameter of 85 km. Ignoring absorption by the atmosphere, what is the intensity of the light
(a) Just outside the laser
(b) Where it hits the surface of the Moon?