-1/2x^2y-1/3xy^2+1/2yx^2+2/3y^2x-4/5x^2y
=(-1/2+1/2-4/5)x²y+(2/3-1/3)xy²
=-4/5x²y+1/3xy²
=-4/5x(-5)²x(-3)+1/3x(-5)x(-3)²
=60-15
=45