[1/2xy(x^2+y)(x^2-y)+3/2x^2y^7÷3xy^4]÷(-1/8x^4y)
=[1/2xy(x^4-y^2)+1/2xy^3]÷(-1/8x^4y)
=[1/2x^5y-1/2xy^3+1/2y^3]÷(-1/8x^4y)
=(1/2x^5y)÷(-1/8x^4y)
=-4x