Answer: If you mean the mapping y(x) := 3x+4, then y(x) is not linear, because it does not satisfy the two properties of linearity. Only equations of the form y(x) := ax (for "a" being any real or complex number) are linear. Don't be confused with the plot of the graph of y(x) = 3x+4 being a line - this does not mean linear in the sense of the definition in Linear Algebra. Some authors define such function as "affine-linear".
