You don't need both. GPE is the gravitational potential energy caused by the fact that an object is not touching the ground of the earth. KE is caused by an object moving. This problem says that the bowling ball "sits" meaning that you only need the GPE because it's not moving and it is not touching the surface. You would use the GPE equation to find how much Potential energy an object has. If you want its velocity, you would set the answer to the GPE equation equal to the KE equation to find its velocity.
A vaccum unlike sound,light can travel through any matter including a great vacuum of nothing (space)
c. -98 m/s
The motion of the rock is a uniformly accelerated motion (free fall) with constant acceleration
(negative since it is downward). Therefore, we can find its velocity using the following suvat equation

where
v is the final velocity
u is the initial velocity
g is the acceleration of gravity
t is the time
For the rock in the problem,
u = 0
So, its velocity at t = 10 s is

where the negative sign indicates that the velocity points downward.
d. -490 m
Since the motion is at constant acceleration, we can use another suvat equation:

where
s is the displacement
u is the initial velocity
g is the acceleration of gravity
t is the time
Substituting:
u = 0

t = 10 s
We find the rock's displacement:

where the negative sign means the displacement is downward.