Residents of Hawaii are warned of the approach of a tsunami by sirens mounted on the tops

Question:

Residents of Hawaii are warned of the approach of a tsunami by sirens mounted on the tops of towers. Suppose a siren produces a sound that has an intensity level of 120 dB at a distance of 2.0 m. Treating the siren as a point source of sound, and ignoring reflections and absorption, find the intensity level heard by an observer at a distance of

(a) 12 m

(b) 21 m from the siren.