Hey there! :D
When you are finding the area of corresponding sides, you square the number of the ratio of the similar lengths.
The screens a little blurry, but I'm assuming the corresponding side is represented as:

So, you would keep a and b where they are, (you would be confusing the areas if you switched it in any way) and then just square the variables.
"C" is the best answer. I hope this helps!
~kaikers