Hi,
costs varies linearly with the distance
(1500,510)
(300,366) m = (510-366)/(1500-300) = 144/1200 = 12/100 = .12
y = .12x + b
510 = .12*1500 + b
330 = b
f(x) = .12x + 330
.12x + 330 <$600
.12x < 270
x < 2250mi
slope represents the constant of increase cost/mi
b = $330 relates to the basic cost of owning a vehicle
f(500) = $390
f(1000) = $450
f(2000) = $570