420. Get 450 to be safe.
A 24x24 tile is 4 square feet. You would need 105 of them.
16 x 16 = 256 sq in = 1.777 sq ft 420/1.777 = 237 tiles approximately
420
There are 420/7 = 60
420 decimeters is 4200cm
420 ft = 128m
420 / 7 = 60
420 ÷ 15 = 28
420 mm = 16.5 inches