hello
segment addition postulate implies given two points and a third point between them, the sum of the first two point equals the distance of ot the third point.
i'll explain better using the question given
[tex]\begin{gathered} DN=DO+OW+WN \\ we\text{ can also say} \\ DW=DO+OW \\ ON=OW+WN \end{gathered}[/tex]
given a line DN with segment O and W, the sum of DO + OW + WN = DN
