A hill road rises uniformly so that its elevation above a reference level is represented by a straight line when graphed against horizontal distance. On a certain survey drawing, the road is shown to be 2m above the reference level at the origin and 20m above the reference level at a horizontal distance of 90m.
(i) Taking the horizontal distance x (in metres) along the road as the independent variable and the elevation y (in metres) as the dependent variable, write the equation of the line representing the road.
(ii) Using this equation, find the elevation of the road at a horizontal distance of 45m.
(iii) Determine how far (horizontally) from the origin the road will first reach an elevation of 50m.