Question 37555
If we let x be km traveled and y be the cost (in $), we have been given two points, (x, y).  These points are (200, 65) and (350, 80).  We treat these as any two (x, y) points.  Let us first find the slope:
m = (y2 - y1) / (x2 - x1)
m = (80 - 65) / (350 - 200)
m = 15 / 150
m = 0.10
Now we use the point slope form to get the equation of the line:
y - y1 = m(x - x1)  now plug in
y - 65 = .1(x - 200)
y - 65 = .1x - 20
y = .1x + 45
This IS the correct answer, not what you have.  Notice the difference between .1 and .01
b) Now plug in x = 500
y = .1x + 45
y = .1(500) + 45
y = 50 + 45
y = 95
There you go...