1) (m^3+6n^2)^2-(6n^2m^3)^2
3) (9z+2x^4)^2-(2x^4-9z)^2

(m^3+6n^2)^2-(6n^2m^3)^2=2m^3*12n^2=24m^3 n^2

(9z+2x^4)^2-(2x^4-9z)^2=18z*4x^4=72x^4 z