Hey Batala426,
If the room is 45m x 15m, then the total area is 675 metres squared.
Each tile is 50cm x 1m, so the area of each one is 0.5 metres squared.
675 / 0.5 = 1350
So the least number of tiles you need to pave the whole room is 1350 tiles.
Hope this helps!
Chen :D