jmc

$\lceil (3.6{)}^2\rceil =\lceil 12.96\rceil =13$ because the least integer greater than $12.96$ is $13$. $(\lceil 3.6\rceil {)}^2=4^2=16$ because the least integer greater than $3.6$ is $4$. Therefore, the answer is $13-16=\boxed{-3}$.