PQRS is a trapezium with PQ = 2SR. \(\overrightarrow{PQ}=2\mathbf a,\quad\overrightarrow{PS}=\mathbf b\).

(a) Find \(\overrightarrow{QR}\) in terms of a and b, simplified. [2]

\(\overrightarrow{OX}=\mathbf x,\quad\overrightarrow{OY}=\mathbf y\). M lies on XY with XM : MY = 3 : 5.

(b) Find \(\overrightarrow{OM}\) in simplest form. [2]