How did the northwest ordinance of 1787 affect slavery?

How did northern leaders try to encourage americans to buy goods made in the united states rather than foreign import? a. high taxes on imports to increase the cost of imported goods b. low taxes on imports to increase the cost of imported goods c. high taxes on imports to decrease the cost of imported goods od low taxes on imports to decrease the cost of imported goods e high taxes on imports to decrease the cost of manufactured goods