A student is standing 8 m from a roaring truck engine that is measured at 20 dB. The student moves 4 m closer to the engine. What is the measured sound intensity at the new distance? (dB) Can you also explain why? I need to know how to do it and I don't know how to.

Sally turns on her cellular telephone to speak to her friend who is located thousands of miles away. which of the following best describes how such a telephone is able to transmit and receive information? a. the cellular telephone transmits, receives, and encodes information using only sound waves. b. the cellular telephone transmits, receives, and encodes information using only electromagnetic waves. c. the cellular telephone transmits information by electromagnetic waves to a receiver which then encodes them and produces sound. d. the cellular telephone transmits information by sound waves to a receiver which then encodes them and produces electromagnetic waves.