I'm having issues remembering how to create cost functions:

For a long-distance phone call, a hotel charges $9.89 for the first minute and $0.90 for each additional minute or fraction thereof. A formula for the cost is given below, wheret is the time in minutesUse a graphing utility to graph the cost function for 0 <

So the function is ?

C(t)=9.89-0.90[[-(t-1)]]

Do I just distribute that out?

t ≤ 5.

How do I set the paramaters for this requirement to graph this on my calculator ?