Try this beautiful problem from the Pre-RMO, 2019 based on Diameter of a circle.
A village has a circular wall around it, and the wall has four gates pointing north, southeast and west. A tree stands outside the village, 16 m north of the north gate, and it can be just seen appearing on the horizon from a point 48 m east of the south gate. Find the diameter in meters of the wall that surrounds the village.
But try the problem first...
Answer: is 48.
PRMO, 2019, Question 25
Geometry Vol I to IV by Hall and Stevens
Let radius =r