:) Well, I dunno about anyone else but this question makes my head spin!
M<J = m<N ( alternate angles)
m<K = m<M ( alternate angles)
so the third angles must also be equal ( total 180 degrees in each triangle)
Therefor the triangles are similar
Yes
The rule to check if a triplet of numbers can represent the sides of a triangle is the following: the sum of the length of two sides must exceed the third one.
This happens for all possible couples in your case:



Let the number x.
Then the number divided by 2 gives

Subtract 3.8 from the quotient gives

Hence,


x = 21.6