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 50 minutes of calls is $13.98 and the monthly cost for 78 minutes is $17.06 . What is the monthly cost for 77 minutes of calls?
y = mx + b slope(m) = 0.11 use either of ur points...(50,13.98)...x = 50 and y = 13.98 now sub into the formula and find b, the y int 13.98 = 0.11(50) + b 13.98 = 5.5 + b 13.98 - 5.5 = b 8.48 = b
so ur equation is : y = 0.11x + 8.48.......for 77 minutes...sub in 77 for x y = 0.11(77) + 8.48 y = 8.47 + 8.48 y = 16.95 <=== this is the cost for 77 minutes
