Answer
$(a)$. $AD$ is undefined.
$(b)$. $DA$$=$$[14$ $-14]$
Work Step by Step
$(a)$. $AD$ is undefined because, $A$ has dimensions $2×2$ and $D$ has dimensions $1×2$ so the columns of $A$ won't match the rows of $D$.
$(b)$. $DA$ is defined view image below.
