Answer
$$ - 30i$$
Work Step by Step
$$\eqalign{
& \left[ {5\left( {\cos {{90}^ \circ } + i\sin {{90}^ \circ }} \right)} \right]\left[ {6\left( {\cos {{180}^ \circ } + i\sin {{180}^ \circ }} \right)} \right] \cr
& {\text{Write in the rectangular form}} \cr
& {\text{ = }}\left[ {5\left( {0 + i\left( 1 \right)} \right)} \right]\left[ {6\left( { - 1 + i\left( 0 \right)} \right)} \right] \cr
& {\text{Multiply}} \cr
& {\text{ = }}\left[ {5\left( i \right)} \right]\left[ {6\left( { - 1} \right)} \right] \cr
& {\text{ = }} - 30i \cr} $$
