They way to find the y-intercept from two points is to first find the slope, which can be derived from the formula [tex]m=\frac{y_2-y_1}{x_2-x_1}[/tex].
Then, you can plug in one of the two points [tex](x_1,y_1)[/tex] or [tex](x_2,y_2)[/tex] into the formula y=mx+b to solve for b, which is your y-intercept.