\[90a^{4}b^{3} \cdot \left( - 3\frac{1}{3}ab^{6} \right)^{2} =\]
\[= 90a^{4}b^{3} \cdot \left( - \frac{10}{3} \right)^{2}a^{2}b^{12} =\]
\[= 90 \cdot \frac{100}{9}a^{6}b^{15} = 1000a^{6}b^{15}.\]