Answer
Loudness = $112$ $decibels$
Work Step by Step
Since loudness varies INVERSELY with the square of the distance from the speaker, we can express this in the following manner:
$$ld^{2} = k$$
where $l$ is the loudness of the stereo speaker, $d^{2}$ is the square of the distance from the speaker and $k$ is a proportionality constant. Since we know that, when $d=8$, $l=28$, we can find $k$:
$$k=ld^{2} = (28)(8^{2}) = (28)(64) = 1792$$
and finally answer the question:
$$l = \frac{1,792}{4^{2}} = \frac{1,792}{16} = 112$$
