Answer:
The correct answer is d Both the observer's are correct
Explanation:
We know by postulates of relativity that laws of physics are same in different inertial frames.
Thus for each of the frames they make observations related to their frames and since the observations are true for their individual frames they both are correct. But when we compare the two frames we need to use transformation equations to compare both the results.
To solve this problem we will apply the linear motion kinematic equations. From the definition of the final velocity, as the sum between the initial velocity and the product between the acceleration (gravity) by time, we will find the final velocity. From the second law of kinematics, we will find the vertical position traveled.

Here,
v = Final velocity
= Initial velocity
g = Acceleration due to gravity
t = Time
At t = 4s, v = -30m/s (Downward)
Therefore the initial velocity will be


Now the position can be calculated as,

When it has the ground, y=0 and the time is t=4s,


Therefore the cliff was initially to 41.6m from the ground
Speed is just how fast the object is moving, while velocity is the speed and <em>direction </em>of the object.
edit* Direction would be something such as North, East, etc.