A historic museum charges a rental fee plus $2 per hour for an audio tour guide. The total cost for 4 hours is $12. Find and interpret the rate of change and initial value.

We can represent this problem with the following linear equation

y = 2x + 4

where

y: total cost

x: number of hours

the slope of the line is

m = 2

Which means that for every hour of audio tour guide they charge $ 2.

For "zero" hours (x = 0) a rental fee of $ 4 must be paid.