Deep-water waves with a wave length of 20 m propagate down-river towards the West, in the same direction as a 1.2 m/s river current. (a) What is the wave speed relative to an observer in a boat that is travelling at 2.0 m/s down-river (towards the West)? (b) What is the wave speed relative to an observer in a boat that is travelling at 2.0 m/s towards the Southwest