Q18An equal number of desks and bookcases are to be placed along a library wall that is 15 meters long. Each desk is 2 meters long, and each bookshelf is 1.5 meters long. If the maximum possible number of desks and bookcases are to be placed along the wall, then the space along the wall that is left over will be how many meters long?

A.0.5

B.1

C.1.5

D.2

E.3

怎么算出答案b, 2d+1.5b+r=15, r is left meters,

b=10,d=0,r=0; 答案没有出现

b=9,d=0,r=1.5; C

b=8,d=1,r=1;  B

b=6,d=3,r=0

why choose B?