Answer:
Length NJ = x = 3
Explanation:
Since the pentagons are similar, the ratio of each side of pentagon ABCDE to the corresponding side of pentagon JKLMN must be the same for all sides
Therefore

From the values provided for the lengths of the sides of the two pentagons this works out to:

Each of the computable ratios = 2
This means
each side of pentagon ABCDE = 2 x each side of pentagon JKLMN
Therefore we get
EA = 2 · NJ
6 = 2 x
x2x = 6
x = 6/2
x = 3
Note
I did not have to calculate all ratios. If the pentagons are similar, the ratios of the sides must be the same and therefore I needed to calculate only one ratio.
I wanted to cover all bases and make sure you understood