The y-intercept appears to be at y=-1. The line appears to also go through grid point (3, 1), which is 2 units up and 3 units over. The slope is 2/3.
In slope-intercept form the equation of the line is
y = (2/3)x - 1
You need to subtract:
52,000,000
- 31
---------------------------
51999969
N = 10*27 / 87 = 270/18 = 15
