Find the Exact Value of the Expression $- 2$ B) $\frac { 2 \sqrt { 3 } } { 3 }$

Multiple Choice

Find the exact value of the expression.
-csc 840°

A) $- 2$
B) $\frac { 2 \sqrt { 3 } } { 3 }$
C) $\sqrt { 2 }$
D) $- \frac { \sqrt { 3 } } { 3 }$