3/4a^4b^7+1/2a^3b^8-1/9a^2b^4）/[-(1/3 ab^3]^2
=(3/4a^4b^7+1/2a^3b^8-1/9a^2b^4）/[-(1/9 a^2b^6]
=3/4a^4b^7/[-(1/9 a^2b^6]+1/2a^3b^8/[-(1/9 a^2b^6]-1/9a^2b^4/[-(1/9 a^2b^6]
=-27/4a^2b-9/2ab^2+1/b^2
=27/4-36+1/16
=-467/16