If two similar triangles have side lengths 3cm and 7cm then we can determine that the scale factor for the lengths is: 7/3
Now, we have to work out the area scale factor !
This is simple, since area is given in cm² then all we have to do is square our original scale factor!
So,
7/3² = 49/9
So, we can say that the ratio of the area would be:
x : 49/9x
Hope this helps! <3