What piece of legislation stated that slavery was banned north of the 36'30 and south of the 36'30 slavery would be allowed

The Missouri Compromise of 1820 established the latitude 36°30′ as the northern limit for slavery to be legal in the territories of the west.

Explanation:

The Missouri Compromise, as it was known, would remain in impact for just over 30 years till the Kansas-Nebraska act of 1854 revoked it. In 1857, the Supreme Court in Dred Scott's case found the agreement unconstitutional, setting the stage for the nation's final journey through the Civil War. In 1820, while growing sectional tensions over the slavery issue, the U. S. Congress passed a law welcoming Missouri to the Union as a captive state and free state.