(3/4a^4b^7+1/18a^3b^8-1/9a^2b^6)÷(-1/3ab^3)^2
=(3/4a^4b^7+1/18a^3b^8-1/9a^2b^6)÷(-1/9a^2b^6)
=3/4a^4b^7÷(-1/9a^2b^6)+1/18a^3b^8÷(-1/9a^2b^6)-1/9a^2b^6÷(-1/9a^2b^6)
=-27/4a^2b-1/2ab^2+1
=27/4-4+1
=15/4
(3/4a^4b^7+1/18a^3b^8-1/9a^2b^6)÷(-1/3ab^3)^2
=(3/4a^4b^7+1/18a^3b^8-1/9a^2b^6)÷(-1/9a^2b^6)
=3/4a^4b^7÷(-1/9a^2b^6)+1/18a^3b^8÷(-1/9a^2b^6)-1/9a^2b^6÷(-1/9a^2b^6)
=-27/4a^2b-1/2ab^2+1
=27/4-4+1
=15/4