sometimes it helps to draw it...so u can see
7 7
J_______K_________L
|__________________|
4x - 2
since K is the midpoint, it splits the segment in 2 equal parts
JK + KL = JL
7 + 7 = 4x - 2
14 = 4x - 2
14 + 2 = 4x
16 = 4x
16/4 = x
4 = x <====
KL = 7 <===
JL = 4x - 2....4(4) - 2.....16 - 2 = 14 <==