You are multiplying by 4 each time.
1) -3 x 4 = -12
2) -12 x 4 = -48
3) -48 x 4 = -192
4) -192 x 4 = -768
5) -768 x 4 = -3072
6) -3072 x 4 = -12288
7) -12288 x 4 = - 49152
8) -12288 x 4 = -196608
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D) -196,608 is your 8th term.
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hope this helps