3) If two incoherent sources operating give levels of 88 dB and 75 dB re 1 Pa at a given observer position when they are operated individually, what is the level when both sources are operating. 4) If the two sources in 3) are of the same frequency and are in phase, what is the level when both sources are operating? 5) If a source emits 1W of sound power in shallow water of depth 10m, what is the Sound Intensity Level in dB re 10-2 watts/m at a horizontal distance of 100m, 200m and 400m from the source? What are the corresponding SPL levels in dB re 1 Pa.