Robert, a stuntman, projects himself from a height of 50.0 meters in a horizontal direction. he safely lands at a horizontal distance of 100.0 meters. calculate the horizontal velocity with which robert projected himself.

To get this we need to know how long he was traveling. To know that we need to solve for the time it took for him to hit the ground. This is given by the vertical height he started at and the equation of motion for falling objects. The position function is
Y= -(9.8/2)t^2 + 50 = 0
t=3.19s
That's how long he's in the air. When he hits the ground he stops moving forward so this is also the amount of time he was moving at 100m/s horizontally. Now use speed distance relationship
X=vt
And solve for v
100m/3.19s = 31.35m/s

31.34 is the answer. or 31.35 which ever you have in your answer choices

Independent variable is something that is changed in a experiment.