Connect EF, extend the extension line of intersecting CA at point M, and extend the intersecting green line in the opposite direction at point N..

Measure AE=a, EM=c, MN=d, and let the length of the green line be 2b. From the nature of similar triangles, A/B = c/d, ∴ B = (AD)/C.

So the length of the green line is 2ad/c.