to answer the question asked you can solve a proportion when given two triangles, but in this one I feel somethings missing like its possibly a multiple choice.
I tried every way I could think of and got this 6.5 for the bottom A-B
That is not true. For example, if you take PI . Rounded is 3.14. But if you were to do the square root of pi then it would be an IRRATIONAL number. so it's false. <span />