with points (1900, 120) & (1990, 1048)

use point (1900, 120) to find b

is the y intercept way back at x = 0

you can re-calculate this regression by making for example the year 1900 your new 0 point giving

1) (0, 120)

2) (40, 502)

3) (90, 1048)

This may be a better domain