ANSWER
KM = 17
EXPLANATION
We have that point L is on the line segment KM.
Let us draw a diagram to represent it:
From the diagram, we see that the length of KM is the sum of the lengths of KL and LM.
This means that:
KM = KL + LM
KM = 12 + 5
KM = 17
That is the value of the length of KM.
