Answer
$0.32$
Work Step by Step
We know that $P\left(\text{an event happens}\right)=1-P\left(\text{an event doesn't happen}\right).$
Hence, (with $68\%=0.68$), here we have:
$P(\text{does not own a pet})=1-P(\text{owns a pet})\\
P(\text{does not own a pet})=1-0.68\\
P(\text{does not own a pet})=0.32$