1) 2y(2x-3y)-3y(5y-3x)
= 4xy - 6y^2 - 15y^2 + 9xy
= 4xy + 9xy - 6y^2 - 15y^2
= 13xy - 21y^2
2) a(2a^3 - 3n) - n(2n^2 - a)
= 2a^4 - 3an - 2n^3 + na
= 2a^4 - 2n^3 - 2an + na
= 2a^4 - 2n^3 - a(2n - n)
= 2a^4 - 2n^3 - an
3) b(b^3 - b^2 + b) - (b^3 - b^2 + b)
= b^4 - b^3 + b^2 - b^3 + b^2 - b
= b^4 - 2b^3 + 2b^2 - b