1.

$PQRS$ is a parallelogram.
$\overset{\rightarrow}{PQ}=3a$ and $\overset{\rightarrow}{PS}=2b$.

$T$ is a point on $QS$ such that $QT:TS=1:2$.

Find $\overset{\rightarrow}{QS}$, giving your answer as simply as possible in terms of $a$ and $b$.