please tell me how this done with steps so I can do this on my own as well

Answer:
6
Step-by-step explanation:
Because J is the midpoint of KL, it means that KJ ans JL are equal.
Think about it like this:
Hope this helps!
Step-by-step explanation:
the midpoint of a line splits the line into 2 equally long parts.
therefore, JI must be equally long to KJ.
x = 6
and with KJ = 6 and JI = 6, then KI = KJ + JI = 6+6 = 12