How would i calculate the x from a known velocity when launching a ball off a table?

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.