From the information that I have gathered on Common App, the University of Michigan allows you to submit a maximum of six letters of recommendation (four teachers, two other). However, I have heard conflicting reports about how many letters I should actually submit. Is there a recommended sweet spot? Or is it generally better to reinforce your application with extra recommendations?
The requirement is 1 and it is recommended you send in more only if an additional letter shows a different aspect of your life. For example, an letter from an AP science teacher and a letter from a coach would be a good combo.