Answer:
LM = LN + MN [ assuming N is a point between L and M ]
[tex](x + 7) = (6x - 5) + (3x + 20) \\ x + 7 = 9x + 15 \\ 8x = - 8 \\ { \underline{x = - 1}}[/tex]
then find MN:
[tex]MN = 3x + 20 \\ MN = 3( - 1) + 20 = - 3 + 20\\ { \boxed{ \boxed{MN = 17}}}[/tex]
