Question

How would I calculate the X from a known velocity when launching a ball off a table?

Answer 1

Here are the steps you would need to follow:

#1). Define what 'the 'X is, and how it's related to the ball.
#2). Be clear on how 'the X' is related to the 'known velocity'.
#3). Identify how the 'known velocity' is related to the action of the ball when it's launched.

With this information in front of you, you'll have a much better chance
of answering the question.

With none of it in front of me, I have no chance at all.

Answer 2

Use the equation:

$X=ut+ \frac{1}{2} at^{2}$
where u is the initial velocity, a is the acceleration downwards (in this case $a=g=9.81m s^{-2}$)

Hope this helps :)