to receive monthly payments of 1000 for 25 years how much would a person have to invest now in an annuity with an annual interest rate of 4.2% to achieve this goal

According the inverse square law, doubling the distance from the source of the sound, a speaker, for example, will drop the sound 6 db each time. if you were standing in the back of an auditorium, 32 feet away from a speaker not using any amplification, would you be able to hear a speaker clearly? why or why not?