Well first here we need to take 7.5*5.5=41.25 now this number here is the area of the box now we need to take 41.25/.5 to see how many 1/2 inch area tiles would fit on top of this box, and 41.25/.5=82.5 and that should be your end answer enjoy!=)
(P.s. please let me know if this was correct thanks!=)