A decade is 10 years so eight and a half decades is 85 years.
i can't tell you but here's a hint: there are 10 years in a decade so 85 divided by 10 is......(round 85 to 80)
There are 3.5 decades in 35 years
There are 5 decades in 50 years.
230 years = 23 decades
There are 20 years in two decades.
16 decades and 4 years.
96 decades and 9 years.
There are 19 decades in 190 years.
There are 12 decades in 120 years.
12.2 years = 1.22 decades
There are 10.6 decades. Or 10 decades plus 6 years.