In this item, it is unfortunate that a figure, drawing, or illustration is not given. To be able to answer this, it is assumed that these segments are collinear. Points L, M, and N are collinear, and that L lies between MN.
The length of the whole segment MN is the sum of the length of the subsegments, LN and LM. This can be mathematically expressed,
LN + LM = MN
We are given with the lengths of the smalller segments and substituting the known values,
MN = 54 + 31
MN = 85
ANSWER: MN = 85
