Why can’t we always measure angles in degrees? Why do we have radians?

Apublic library wants to place 4 magazines and 9 books on each display shelf. the expressions 4s +9s represents the total number of items that will be displayed on s shelves. simplify this expression

Can someone me out here and the tell me the greatest common factor

What are the solutions of the system? solve by graphing. y = -x^2 -6x - 7 y = 2