Just need a simple a, b, c, or d answer, you

What is the difference between regular convex and concave polygons

15 and 14.7 are 1 apart, so 15 – 14.7 must be 1.

Two friends are reading books. jimmy reads a book with 21,356 words. his friend bob reads a book with one-and-a-half times as many words. which expression represents the number of words bob reads?