4 - (0) = y
4 - 0 = 4 y = 4
4 - (1) = y
4 - 1 = 3 y = 3
4 - (2) = y
4 - 2 = 2 y = 2
4 - (3) = y
4 - 3 = 1 y = 1
I am not sure, but I think you are talking about the least square method
First using the given two points we can find the slope (m) of the line

Thus the slope of given line is 1.
Using slope and a point (0,1) we can write the equation in point slope form as
y - 1= 1(x-0)
y - 1 = x
The above equation is the point-slope form of the equation.
Cancel the common factors in the numerator and denominator.
Exact Form:
15
Decimal Form:
0.2
hope l helped have a good day