What is the rule for finding the ratio of the areas of two objects if you know the scale?

The square of the scale

Step-by-step explanation:

Scaling

Suppose we know the scale of the distances, for example, r=5. It means that for each centimeter in the drawing, it corresponds to 5 cm in the real object being scaled. If we wanted to find the ratio of the areas, we would need to scale both dimensions and the ratio would be the square of the scale factor. In our example, the ratio of the areas would be 25, i. e. each square centimeter would correspond to 25 square centimeters

The rule for finding the ratio of the areas of two objects: The square of the scale