How long has slavery exsisted

It depends on what you mean because slavery is still alive today unfortunately in other countries. I'm assuming you mean African American slavery in the USA. Your answer would be from the 1600s - 1865. But at the same time, not every state started slavery at the same time. For instance, Georgia didn't start until the 1700s so it varies, but the first state was Massachusetts in 1619.

answer; i believe that the correct answer is (scientific approach)

debating and finalizing the detail of the policy