24) -pq²(-p²-3p²q+2q⁴) =

$$-pq^2(-p^2-3p^2q+2q^4) = -pq^2 \cdot (-p^2) - pq^2 \cdot (-3p^2q) - pq^2 \cdot 2q^4 = p^3q^2 + 3p^3q^3 - 2pq^6$$