Hello, parent looking for the answer to teach my child!

start sketching the situation
Start by finding the difference between MO and NO
[tex]\begin{gathered} MO-NO=MN \\ 8-5=MN \\ MN=3 \end{gathered}[/tex]Then,
[tex]\begin{gathered} MN+NP=MP \\ 3+13=MP \\ MP=16 \end{gathered}[/tex]