Sunlight is type of EM wave. The intensity of EM follows inverse square law.
[tex] \frac{1}{ n^{2} } [/tex]
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:
[tex]9= \frac{1}{ n^{2} } \\ \\ 9 n^{2} =1 \\ \\ n^{2} = \frac{1}{9} \\ \\ n= \frac{1}{3} [/tex]
The intensity is 9 times greater at a distance that is equal to a 1/3 of Earth's distance:
[tex] \frac{1}{3} *1.496* 10^{11} m=4.99* 10^{10} m[/tex]
