The intensity of light​ (in foot-candles) varies inversely as the square of​ x, the distance in feet from the light source.

Question

The intensity of light​ (in foot-candles) varies inversely as the square of​ x, the distance in feet from the light source. The intensity of light 2 feet from the source is ​16 foot-candles. How far away is the source if the intensity of light is ​4 foot-candles?

Answer 1

16 = k/2^2 = k/4

k = 16(4) = 64

4 = 64/x^2

1 =16/x^2

x^2 =16

x = 4 feet away

Answer 2

(16)(2²) = (4)(x²)