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 40 minutes of calls is $12.18 and the monthly cost for 97 minutes is $17.31. What is the monthly cost for 54 minutes of calls?

Answer 1

m (the slope) = (17.31-12.18)/(97-40) = .09
y = mx + b = .09x + b
if i plug a point into the equation, i get b
12.18 = .09(40) + b
b = 11.82
y = .09(54) + 11.82 = $16.68
:)

Answer 2

it was $13.44

Answer 3

sorry molly you're right
i put in calculator 12.18 = .09(4) + b instead of 12.18 = .09(40) + b