## Calculus: Early Transcendentals (2nd Edition)

If 0≤t≤60: $c(t) = 0.05t$ If 60
From 8 to 9 P.M, the cost of the cost per minute is 5 cents or 0.05 dollars. 9 PM. is 60 minutes after 8P.M, so if 0≤t≤60 the function $c(t) = 0.05t$ is appropriate. Now after 9 P.M, the price changes to 3 cents or 0.03 dollars. Notice the question asks states the price changes after 9P.M. That means 9 P.M, or 60 minutes after 8 P.M is not included in the second piece of the function. For this reason we say If 60.