Simplify the Following Expression by Combining Similar Terms $$3 x - 6 x$$

Multiple Choice

Simplify the following expression by combining similar terms. $$3 x - 6 x$$

A) $- 3 x ^ { 2 }$
B) $- 9 x$
C) $9 x$
D) $- 3 x$
E) $- 3$