Kindly look at this question from Greprep: https://greprepclub.com/forum/what-is-the-length-of-hypotenuse-k-7499.html

If we have established that the bigger triangle is 90-45-45 then, it follows that since the place where the two triangles meet is 90, the angle on the two sides of this 90 degree angle must be 45 and 45 in the two triangles.

And if it is that, then the smaller triangle must also be 90-45-45 and if it is that, then k must be x*sqrt2. If x is 7.2 then answer should around 10.41.

Now what am I missing here?