ANSWER:
C = 0.23M + 26
Given:
Peak air time = $0.23 per minute
First bill = $51.30
Minutes of airtime = 110 minutes
The equation that models the cost (C) of your monthly bill in terms of the number of minutes of air time (M) will be:
C = 51.3 = 0.23M + Monthly charge
51.3 = 0.23(110) + Monthly charge
Solve for monthly charge:
Monthly charge = $26
The equation is:
C = 0.23M + 26