How to remove last x chars of an element in list : I have a long list of numbers...

Something like 
num_list = 
["9222111X 9555222X", "9777666X 9555111X", "9333555X 9444222X"]..

I'd like to remove the last x elements of a list to make every element in my list the same length.

I'd like to remove all the numbers after the "X" leaving only 4. Like this:

num_list = 
["9222X 9555X", "9777X 9555X", "9333X 9444X"]