Answer:
Let's assume that Susan's graph is linear. Then, we can do linear interpolation. Let y be the amount charged for 10 hours of work done:
(7-10)/(7-11) = (168-y)/(168-264)
y = $240
For Jim's Lawn care, let's find the constant slope using points (1,20) and (2,40):
m = (20 - 40)/(1-2) = 20
Then, since the y-intercept is zero, the linear equation is:
y = 20x
Substituting x = 10 hours,
y = 20(10) = $200
The difference between the two would then be:
Difference = $240 - $200 = $40
