A horizontal straight line is drawn parallel to the x-axis such that it passes through the point (0,4).
(i) Determine the slope of this line.
(ii) Write the equation of the line.
(iii) State the angle of inclination that the line makes with the positive direction of the x-axis.
(iv) Explain why the equation of this line cannot be expressed in the form y=mx+c with a non-zero value of m.