Factorise

$125 x^{3}-27 y^{3}-225 x^{2} y+135 x y^{2}=(5 x)^{3}-(3 y)^{3}-3(5 x)^{2}(3 y)+3(5 x)(3 y)^{2}$

$=(5 x-3 y)^{3}$

Hence, factorisation of $125 x^{3}-27 y^{3}-225 x^{2} y+135 x y^{2}$ is $(5 x-3 y)^{3}$.