The answer is 6:5 because the ratio of the areas of the rectangle to the square is given as 1.2. This means that for every 1.2 units of area in the rectangle, there is 1 unit of area in the square.

To simplify this ratio, we can multiply both sides by 5 to get rid of the decimal:

1.2 * 5 = 6

So, for every 6 units of area in the rectangle, there are 5 units of area in the square. This can be written as the ratio 6:5.