If m is between l and n, ln=3x–1, lm=4, and mn=x–1, what is the value of x and mn?

M is the midpoint of the line. Imagine a line LN with a midpoint of M in the middle.

So,

4+x-1= 3x-1 (the two half segments equal the whole line)

Combine like terms.

3+x= 3x-1

Add one to the other side.

4+x= 3x

Subtract x on both sides.

4=2x

Divide by 2.

x=2 

I hope this helps!
~kaikers