A surveyor models two straight stretches of road on a city map as follows.
a. (i) The first road segment is represented by 4x+3y−60=0. Find its slope.
b. (ii) The second road segment is represented by 3x−4y+12=0. Determine, with justification, whether the two road segments are perpendicular to each other.
c. (iii) Calculate the y-intercept of the first road segment and interpret its meaning on the map, where x measures distance eastwards and y measures distance northwards in kilometres.