\[b_{1} = 3;\ \ q = - 2;\ \ b_{n} = b_{1} \cdot q^{n - 1}\]
\[b_{6} = 3 \cdot ( - 2)^{5} =\]
\[= 3 \cdot ( - 32) = - 96\]
\[Ответ:b_{6} = - 96\]