Similar triangles are triangles which have the same shape but not the same size. This means their angle measures are equal but their side lengths are not instead they are proportional. This means that if a rectangle has sides 3 by 4 its area will be 12. But its image after being dilated by 2 is 6 by 8 or twice the side. Will the area also be twice the size? The area of the image is 6*8 = 48. This is 4 times bigger than 12. Not twice as big. So the similarity of the area is the scale factor squared.
So if figure A has area 13 units. And they have a ratio or scale factor of 1/8 then the area sclae factor will be 1/8*1/8 = 1/64.
