Solve for the length of the midsegment.
The mid segment is right between the lengths of the end segments.....it equals the 'average'
( 4n+6 + 2n-2 ) /2 = n+ 12
(6n +4)/2 = n+ 12
3n + 2 = n+ 12
2n = 10
n = 5 use this 'n' to calc the line lengths