[(-3mn)^2*m^3-2m^2(3mn^2)^3*0.5n]/(-3m^2n)^2
=[9*m^2*n^2*m^3-2*m^2*27*m^3*n^6*0.5n]/ (9*m^4n^2)
=m-3mn^5
=10-3*10*1^5
=10-30
=-20