Pablo was reviewing the water bill for his carwash business and determined that the highest bill, $5,000, occurred in july when 4,000 cars were washed and the lowest bill, $4,000, occurred in february when 2,000 cars were washed. what was the fixed portion of the water bill?

The easiest way to solve this is to work with two equations:

X + 4000Y = $5000 (1)

X + 2000Y = $4000 (2)

Where X is the fixed portion of the water bill and Y is the cost of water per car.

Solve for X for each equation:

X = $5000 - 4000Y (3)

X = $4000 - 2000Y (4)

Therefore:

$5000 - 4000Y = $4000 - 2000Y (5)

Solve for Y:

Y = $0.5

Substitute into equation1:

X + 4000 (0.5) = $5000

X = $3000