A 1000-Hz tone from a loudspeaker has an intensity level of 100 dB at a distance of

Question:

A 1000-Hz tone from a loudspeaker has an intensity level of 100 dB at a distance of 2.5 m. If the speaker is assumed to be a point source, how far from the speaker will the sound have intensity levels
(a) Of 60 dB and
(b) Barely high enough to be heard?