4y^4-4x^3+0.2x^2y^2+xy^3-1/5x^2y^2-4y^4-x^3y
=-4x^3+xy^3-x^3y
=-4×(-2)^3+(-2)×0.3^3-(-2)^3×0.3
=32-0.054+2.4
=34.346