`(4^6. 9^5+6^9. 120)/(8^4. 3^12-6^11)`
`=((2^2)^6. (3^2)^5+2^12. 3^10. 5)/((2^3)^4. 3^12-6^11)`
`=(2^12. 3^10+2^12. 3^10 .5)/(2^12 .3^12-6^11)`
`=(2^12. 3^10.(1+5))/(6^12-6^11)`
`=(2^12. 3^10.(1+5))/(6^11.(6-1))`
`=(2^12. 3^10. 2.3)/(6^11. 5)`
`=(2^13. 3^11)/(6^11. 5)`
`=(2^2 .6^11)/(6^11. 5)`
`=4/5`