Why were Africans interested in trading slaves with the Europeans?

Because they got to trade the slaves for items they needed (e.g.) firearms, materials (etc.). So the Europeans didn't have the power to just march in and kidnap Africans to make them slaves, so they provided a trade that would benefit both parties, the Africans got materials they needed and the Europeans got the slaves.

I hope this helps.

both are true, the congress does have the power to create banks, even if this power is not specifically described in the constitution, since there is nothing restricting it and there is power given to the congress to make "all laws which shall be necessary and proper". maryland was not allowed to tax a branch of the national bank operating there, and the supreme court decided that no state could. both of these topics were discussed in a decision of the mcculloch v. maryland case in 1819.