The land ordinance of 1785 affected slavery by
stopping it from spreading.
spreading it throughout the nation.
abolishing it throughout the nation.
allowing enslaved people to settle in the west.

The Land Ordinance of 1785 affected slavery by stopping it from spreading.

Explanation:

After the United States got hold after the land in the west which it got through the treaty of Paris, the United States Congress shortly passed an ordinance that established the regulations that regulated the division of lands in the west among the settlers willing to settle there.

According to this ordinance, an area with more than 60,000 population could ask for statehood and slavery in such area would be banned. This ordinance was in force until the Homestead Act of 1862 was implemented.