assume' not working with find(x,y,z) ...?

I was solving a simple geometry problem for my son... I reduced the problem to a set of 3 equations with 3 positive unknown variables ( 3 distances so they need to be positive) .

Using the symbolic engine, Mathcad 14.0 has no problem finding a set of 4 solutions... including the one I was looking for , with positive numbers.

So I wanted to add the constraint that the solution had to be real and positive using the modifier "assume, ALL = RealRange(0,100))" in conjunction with the Given and Find(a,b.c) block.

I know that the syntax "assume, ALL = RealRange(0,100))" works when trying to simplify one single equation with multiple variables as shown in the tutorials, but it seems to be ignored in the context of a Given and Find block...

Maybe somebody can tell me what I am doing wrong in the attached file.

Thanks

sylvain flamant