Line MN and Line KL are parallel.
JM = 8
MK = 40
NL = 30
If JM is 8 and MK is 40, the multiplier is 5, since Line MN and Line KL are parallel.
This means that Line NJ's length is 5 times LESS than Line NL.
Divide 30 by 5 to solve for Line NJ.
30 / 5 = 6.
Line NJ is 6.
I hope this helps!