a student presses a book between his hands, as the drawing indicates. the forces that he exerts on the front back covers of the book are...

a student presses a book between his hands, as the drawing indicates. the forces that he exerts on the front & back covers of the book are perpindicular to teh book and are horizontal. the book weighs 31 N. the coefficient of static friction between his hands and the book is .4. to keep the book from falling, what is the magnitude of the minimum pressing force that each hand must exert?