81^2x÷9^2x÷3^x=729
(3^4)^2x÷(3^2)^2x÷3^x=3^6
3^8x÷3^4x÷3^x=3^6
3^(8x-4x-x)=3^6
3^3x=3^6
3x=6
x=2