Answer:
45 cm
Explanation:
Find LCM(15,9). First factor both numbers:
So,
This means that the length of the side of the smallest square area that can be covered by these tiles is 45 cm.
Practically, you can put 3 tiles in a row (to make 3 lenghts of 15 cm each that add up to 45 cm) and put such 5 rows (to make 5 lengths of 9 cm that add up to 45 cm).