Answer :
The monthly cost for 66 minutes of calls will be $15.84.
Monthly cost is the payment or the bill amount that needs to be paid at the end of the month.
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 45 minutes of calls = $14.40
The monthly cost for 102 minutes = $19.53
The above values can be paired in groups so as to satisfies the coordinates of a linear function
(45,14.40) and (102,19.53)
Finding the slope of the graph using these points
slope, m=Δy/Δx
m=Δy=19.53 - 14.40 = 5.13
Δx=102 - 45 = 57
m = 5.13/57 =0.09
Finding the equation of the linear function using m = 0.09, and point (45,14.40)
m=Δy/Δx
0.09=y-14.40/x-45
0.09(x-45)=y-14.40
0.09x-4.05=y-14.40
0.09x-4.5+14.40=y
y=0.09x + 9.9
So for 66 minutes, the cost will be;
x = 66, y = ?
y=0.09*66 + 9.9
y=5.94+9.9 = $15.84
The monthly cost for 66 minutes of calls is $15.84.
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