The linear function which models the monthly cost and the total cost of using 13 minutes in a month are :
- f(x) = 4.50 + 0.75x
- f(x) = $11.91
Given the Parameters :
- Fixed cost per month = $4.50
- Variable cost per minute = $0.57
The monthly cost, f(x) expressed as a function of the number of minutes used can be expressed thus :
Total cost = Fixed cost + (cost per minute × number of minutes)
f(x) = 4.50 + 0.57x
The cost of using 13 minutes in a month would be :
Substitute the value of x = 13 into the equation :
f(13) = 4.50 + 0.57(13)
f(13) = 4.50 + 7.41
f(13) = $11.91
Therefore, using the cell phone for 13 minutes will cost $11.91.
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