5. Simplify the expression \( \frac{16ab^4}{-56a^3b^3} \).

Divide numerator and denominator by their common factors: \( \frac{16}{-56} = \frac{-2}{7} \), \( a \) reduces to \( a^{-2} \), and \( b^4 \) reduces to \( b \). The result is \( \frac{-2b}{7a^2} \).