Answer:
Pretty Simple!
Now that you know about ratios and all that, this is pretty tame compared to the last problem.
Now, the problem is talking 2D(2 Dimensions)
The ratio is not going to work because it has only one parameter.
Thus, we need to square it!
Thus, we have your correct ratio.
Now, we only need to do the same thing for the triangle problem. Meaning that, we need to compare the ratios, with x as the thing we are looking for.
See? X is practically handed to us.
Hope this helps!