Reddit Math Puzzle

So it’s not nonlinear math, but this made for a fun five minutes over Sunday morning coffee. There’s a number of ways of solving it, I went for the geometric one myself but the same answer comes out in the end for all of them, hopefully And it’s nice to think you could still pass the Leaving Cert if you had to sit it again tomorrow, so hooray for Reddit.

Enjoy over coffee today! (My scribbled answer after the break…)

3.05572809 (or for those who like a more neat answer, 4(3-√5) )