A company hires $11$ new employees, and they will be assigned to four different departments, A, B, C, D. Each department has at least one new employee. In how many ways can these assignments be done?
I know that for each section (A,B,C,D) I should add a () and as long as every section must get a new employee we should start like this: $$(x+x^2/2!+x^3/3!+...)^4$$ then if we look it's $(e^x-1)^4$. After this step I don't know what to do.