The answer is psychoacoustics in which it is the study of the psychological associates the physical measurements of acoustics and it is a branch of psychophysics. In addition to perception, audibility threshold is the lowermost sound pressure level that can be reliably noticed at a given frequency and temporal integration the procedure by which a sound at a constant level is alleged as being louder when it is of the greater period.
This sounds like a Revenue this is typically collected through taxes.
For the monthly fee, we first have to subtract the installation fee of 85 from the total cost for two years which is 685. Why? Because an installation fee is a one time thing. You don't install every year. So less the installation fee, our internet service cost for two years is 600. To make things easier, lets get the service costs for one year. Divide 600 by 2 and you will get 300. 300 is the cost of the internet for a whole year. Divide this by 12 (12 months in a year) and you will get 25. The monthly cost is $25.