4)(2/3x-3y)^3
5)(1/3m+1/2n)^3
6)(1/5a+5b)^3

4) 8x^3/27 - 4x^2y + 18xy^2 - 27y^25) m^3/27 + m^2n/6 + mn^2/4 + n^3/86) a^3/125 + 3a^2b/5 + 15ab^2 + 125b^3(a+b)^3=a^3 + 3a^2b + 3ab^2 + b^3