At what distance from the sun is the intensity of sunlight nine times the value at the earth? (the average earth–sun separation is 1.496 1011 m.)

Sunlight is type of EM wave. The intensity of EM follows inverse square law.

This means that the intensity at a distance that is n times greater will be n^2 times smaller.
Now we set this equation to be equal to 9 and we solve it for n:


The intensity is 9 times greater at a distance that is equal to a 1/3 of Earth's distance:

C. naturally in the environment