a plumber charges an initial amount to make a house call plus an hourly rate for the time he is working. A 1 hour job cots $90 and a 3 hour job costs $210. What is the initial amount and the hourly rate that the plumber charges.

Step-by-step explanation:

(1,90), (3,210)

slope = (210 - 90) / (3 - 1) = 120/2 = 60

y = mx + b

slope (m) = 60

(1,90) ... x = 1 and y = 90

solve for b, the y int (or the initial amount)

90 = 60 (1) + b

90 = 60 + b

90 - 60 = b

30 = b

y = 60x + 30

hourly rate = $ 60

initial amount = $ 30