Rectangular floor of a room is completely tiled with whole tiles, each of which is 15cm square. The black tiles ...

Rectangular floor of a room is completely tiled with whole tiles, each of which is 15cm square. The black tiles form a border of width one tile round the room. Within the black border all the tiles are red. There are exactly twice as many red tiles as black tiles. Determine the possible lengths and corresponding widths for the room.