A concession stand stocks 18 cases of soda for the weekend 6 1/3 cases of soda were sold on Friday, 5 3/4 on Saturday, and 4 1/2 on Sunday. How many cases remain?
a.1 and 5/12 cases
b.2 and 7/8 cases
c.1 and 1/2 cases
d.3 cases