Find the Indicated Term of the Sequence $- 6$ , Find $a _ { 1 }$

Multiple Choice

Find the indicated term of the sequence.
-If the third term of a geometric progression is 3 and the fourth term is $- 6$ , find $a _ { 1 }$ and $r$ .

A) $a _ { 1 } = 12 ; r = - 2$
B) $a _ { 1 } = - \frac { 3 } { 2 } ; r = - 2$
C) $a _ { 1 } = - \frac { 3 } { 4 } ; r = 2$
D) $\mathrm { a } _ { 1 } = \frac { 3 } { 4 } ; \mathrm { r } = - 2$