Please answer this word problem and show the steps please

Question

The intensity of illumination (I) of a light source varies inversely as the square of the distance (d) from the source. If the Illumination 4 ft from the source is 9 foot candles (fc), find the illumination 6 ft from the source.

Answer 1

I = k/d^2 for some fixed constant k

9 = k/4^2 = k/16 ---> k = 9*16 = 144

So the function is I = 144/d^2

for d=6, I = 144/6^2 = 144/36 = 4