A. 3
You have to know figure out as many sides as possible before setting up the ratio.
On the short leg the entire leg is equal to 20, and some part of the line is labeled as 12. So you do do 20-12 which would equal to 8. So the shorter part of the short leg equals to 8.
Then you do the long leg. The entire leg equals to 35. Some part of the long leg is labeled as 7x. So you can label the other part of the long leg as 35-7x.
Since you have the numbers for the ratio now, you can do the next steps.
The first step is picking a location and then going any direction.
When I solved it, I started at the top and went down.
8/35-7x=12/7x
Then you cross multiply.
8*7x=56x. 12*35-7x=420-84x
56x=430-84x
Add 84x on both sides
140x=420
Divide 140 in both sides
X=3