If you're given ANY set of points, how do you find n?

In method of least squares, the formulas are:

m(sum(xi^2)) + b(sum(xi)) = sum(xi * yi)

m(sum(xi)) +nb = sum(yi)

For example, how would you findnto do the method of least squares, if you're given these set of points?

Eg.

If you're given:

(-3, 0.3)

(-1, -1.1)

(1, -1.9)

(3, -3.2)

(5, -3.7)

is n delta x? or the number of x terms? etc. how do you find n?