Vector addition confusion

I am stuck on this one:



According to me, the only correct answers are

[itex]\vec{r} = \vec{t} - \vec{s} \\ \vec{r} + \vec{s} = \vec{t}[/itex]

But according to the key, these are also correct

[itex]\vec{r} + \vec{t} = \vec{s} \\ \vec{s} + \vec{t} = \vec{r} [/itex]

I honestly do not see how, can somebody please explain?