(not sure )
my method
let projection of b onto line dq be M
BM is 2r
then let the remaining angle ( right) be K
in triangle BMK ,
MK = 29-5-r
By Pyth. theorem ,
23^2 = (2r)^2+(29-5-r)^2
529=4r^2+576-48r+r^2
5r^2-48r+47=0
r = 8.493237063 or 1.106762937(rejected)
