In the figure, $P Q R S$ is a trapezium with $P Q$ parallel to $S R$.
The diagonals of the trapezium meet at $X$.
$U$ lies on $S P$ and $T$ lies on $R Q$ such that $U T$ is a line segment through $X$ parallel to $P Q$.
The length of $P Q$ is 12 cm and the length of $S R$ is 3 cm .
What, in centimetres, is the length of UT?