Question

(100, 18,000)
(200, 37,000)
(300, 48,000)
(400, 66,000)
Write an equation for the line that models the data.

Answer 1

maybe it'd be easier without all the zeros:

1 18
2 37
3 48
4 66

y=17x comes close. The errors are

1 +1
2 +3
3 +1
4 -2

Use your favorite regression tool for a more exact line. The best-fit line is

y = 15.5x + 3.5

a good calculator and grapher is at

http://www.alcula.com/calculators/statistics/linear-regression/

It requires at least 5 data points, though so enter 5,81 as a 5th point, since it is exactly on the line of best fit.