(2/3x^4y^7-1/9x^2y^6)÷(-1/3xy^3)^2
=(2/3x^4y^7-1/9x^2y^6)÷(1/9x^2y^6)
=(2/3x^4y^7)÷(1/9x^2y^6)-(1/9x^2y^6)÷(1/9x^2y^6)
=(2/3)*9x^(4-2)y^(7-6)-(1/9)*9x^(2-2)y^(6-6)
=6x^2y-1*x^0y^0
=6x^2y-1*1*1
=6x^2y-1