Answer
45 foot-candles
Work Step by Step
Consider $ I $ to be the intensity and $ d $ to be the distance of the source.
We have $ I=\dfrac{k}{d^2}$ ....(1)
so, $20=\dfrac{k}{225}$
This implies that $ k=4500$
Equation (1) becomes: $ I=\dfrac{4500}{(10)^2}=45$
Therefore, the intensity of a light at a distance 10 feet from the source is 45 foot-candles.
