Use the distributive property of multiplication to simplify.
[tex] (3a^2 - b^4)(-8ab^3) [/tex]
[tex] (3a^2(-8ab^3) - b^4(-8ab^3) [/tex]
[tex] -24a^3b^3 - (-8ab^7) [/tex]
[tex] -24a^3b^3 + 8ab^7 [/tex]