Let $z _ { 1 } = 4 \left( \cos \frac { \pi } { 6 } + i \sin \frac { \pi } { 6 } \right)$

Multiple Choice

Let $z _ { 1 } = 4 \left( \cos \frac { \pi } { 6 } + i \sin \frac { \pi } { 6 } \right)$ and $z _ { 2 } = 5 \left( \cos \frac { \pi } { 3 } + i \sin \frac { \pi } { 3 } \right)$ ) Find $Z _ { 1 } Z _ { 2 }$

A) $20 + i$
B) $20 - 20 i$
C) $20$
D) $0 - 20 i$
E) none