(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)