Three different economics books, two different mathematics books, and one physics book are to be arranged on a bookshelf.

(5) How many arrangements are possible if the books in each subject must all stand together?

(a) 12 (b) 24 (c) 36 (d) 72

(6) How many arrangements are possible if the economics books must stand together?

(a) 24 (b) 36 (c) 144 (d) 288

(7) How many arrangements are possible if the economics books must stand together and to the left of the mathematics and physics books?

(a) 18 (b) 36 (c) 72 (d) 144

(8) How many arrangements by subject are possible if each book is labeled E (economics), M (mathematics), or P (physics)?

(a) 20 (b) 60 (c) 180 (d) 360