Answer
See the figure below.
Work Step by Step
There are many ways to describe this reaction of
$$\rm \overline{p}\;+n\rightarrow\;\;\pi^-+\pi^0$$
since $\pi^0$ could be considered as $ \rm u\; \overline{u}$, or $\rm d\;\overline{d}$.
It can also be considered a combination of $\rm u\;\overline{u}$ and $\rm d \;\overline{d}$.
We chose $\rm u\; \overline{u}$, and the reaction is below.
You can try the other methods since the author did not ask for all of them, he asked only for one.
