The correct answer is LN.
If you rotate triangle NLM, it’s easy to see that lines SR and LN are similar.
Two triangles are similar if the ratio of corresponding sides is the same.
If you take the ratio of the following lines:
LN/MN = SR/RT
Where LN = 4
MN = 2
SR = 8
RT = 4
LN/MN = SR/RT
Plug in the values of each side (line):
4/2 = 8/4
2 = 2
Therefore, line LN is proportional to line SR, while line MN is proportional to line RT.
Thus, the correct answer is LN.