You choose the number of lessons you need depending what skills you want to reach.
6-8 hours for basics driving skills : startings, stops, use of engine brake, turnings, shifting gears up and down, up hill starts.
12-14 hours idem 6-8hours plus maneuvers, highway, urban driving (junctions, priorities, traffic, pedestrians, cyclists.......).
16-20 hours for more indenpendence.