\[- 6b^{2} + b^{3}\ при\ b = - 3.\]
\[- 6b^{2} + b^{3} = b^{2}( - 6 + b) =\]
\[( - 3)^{2} \cdot ( - 6 - 3) = 9 \cdot ( - 9) = - 81.\]