SOLUTION: For this Exercise, assume that a linear equation models each situation. Cell-Phone Charges. The total cost of Tam's cell phone was $410 after 5 months of service and $690 after

Question 991582: For this Exercise, assume that a linear equation models each situation.
Cell-Phone Charges. The total cost of Tam's cell phone was $410 after 5 months of service and $690 after 9 months. What costs had Tam already incurred when her service just began? Assume that Tam's monthly charge is constant.
My answer was $70. The book's answer was $60. Am I right or wrong? Please help me if I'm wrong.
Answer by rothauserc(4718) (Show Source): You can put this solution on YOUR website!
(690 - 410) / 4 = 70, therefore
Tam's cell phone bill is $70 per month, then
690 - (9*70) = 60, therefore
Tam incurred $60 in charges when her service began

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