1. radius of a circle puzzle

I need help with this problem..even asked several friends but no1 knows what to do :[

heres a little picture

so the answer is: 6 - (square- root-10) .. but i have no clue how to even get that.

2. We have $OA=R, \ OB=R-1, \ AB=5-R$
Apply Pitagora in AOB:
$R^2=(R-1)^2+(5-R)^2\Rightarrow R^2-12R+26=0$
Solving for R, the good solution is $R=6-\sqrt{10}$

3. oh wow, thank you very much