According to the article 13 of the articles of confederation, what percentage of votes by the states was required to ratify any amendments

Initially, northerners did not want missouri to be included in the union because 1.) maine would not be allowed to enter the union as a free state 2.) missouri wanted to enter the union as a free state 3.) missouri wanted to enter the union as a slave state 4.) maine would not be allowed to enter the union as a slave state