Answer:
a) Δx = -35ft
b) Δx = -25ft
c) Kyle traveled 10ft more than John
Explanation:
We define a coordinate reference system() in which y = 0 corresponds to the water surface.
a) The initial position of Kyle in our coordinate reference system is:

and his final position is:

Therefore, he traveled
Δx =

b) The initial position of John in our coordinate reference system is:

and his final position is:

Therefore, he traveled
Δx =

c) Then, Kyle traveled 10ft more than John