Answer
$$ - 3 + 3i$$
Work Step by Step
$$\eqalign{
& {\text{Let }}{\bf{u}} = - 3,{\text{ and }}{\bf{v}} = \,3i \cr
& {\text{Find the sum }}{\bf{u}} + {\bf{v}} \cr
& {\bf{w}} = {\bf{u}} + {\bf{v}} \cr
& {\bf{w}} = \left( { - 3} \right) + \left( {\,3i} \right) \cr
& {\bf{w}} = - 3 + 3i \cr
& \cr
& {\text{Graph}} \cr} $$