In this equation (Slope Intercept Form of a linear equation), y = mx + b, which variable relates to the domain and which one relates to the range of a function?

Answer 1

Review the definition here:
http://www.analyzemath.com/DomainRange/DomainRange.html

x relates to the domain and y to the range of the function y(x).

If it were rewritten as x(y) = (y-b)/m, the reverese would be true.