I need help with this old physics problem I got wrong?

Question

At a distance of 12m from a sound source the sound intensity is found to be 0.1W/m^2. What is the sound intensity at a distance 36m from the source?

A. 0.011 W/m^2

B. 0.1 W/m^2

C. 0.3 W/m^2

D. 0.033 W/m^2

After making the assumption to calculate and use the same density I got for 12m, I was apparently wrong to do so, so I found that the answer is not D. I am stumped on what it could be.

Answer 1

36 m is three times 12 m. Since sound intensity falls off like 1/r² , the intensity at 36 m will be 1/9 times the value at 12 m. 0.1 /9 = 0.011111 which rounds to answer A