What is certain is that the shadow is similar to △abc, ∠C = RT∞, AC=4, BC=3, so ab=5, let the height on ab be H, and the ratio of the side of the shadow to the side of △abc is M, then the bottom of the shadow is 5m, the height is hm, and the area of △abc is 6 (provable).

So 5h=2*5m*hm, that's 2m? = 1, m=√2/2, the shadow background is only 5√2/2, and the translation is 5-5m=5-5√2/2.