The monthly cost (in dollars) of a long-distance phone plan is a linear function of the total calling time (in minutes).

Question

The monthly cost (in dollars) of a long-distance phone plan is a linear function of the total calling time (in minutes). The monthly cost for 39

 minutes of calls is $15.93

 and the monthly cost for 92

 minutes is $22.82

. What is the monthly cost for 60

 minutes of calls?

Answer 1

F+39m=15.93

F+92m = 22.82

53m=6.89

m=6.89/53= 13 cents per minute

F=15.93-39(.13)= 15.93-5.07==$10.86 monthly fee

for 60 minutes

10.86+60(.13)= $18.66