Answer
$0.91$
Work Step by Step
We know for a probability that $P(\text{an event happens})=1-P(\text{an event does not happen})$
Since $9\%=0.09$, we have
$P(\text{not shortbread/trefoils})=1-P(\text{shortbread/trefoils})$
This gives:
$P(\text{not shortbread/trefoils})=1-0.09$
So, $P(\text{not shortbread/trefoils})=0.91$
