REVISED ANSWER.
In the picture, I have drawn on the example given. the RC and PD are the same because They are across from each other perfectly. So the answer is still PD=400m but if there can be two answers then I would have to say another possiblity would be 200m for the diameter of the pond. The wording of this problem is tricky and the picture can throw you off a bit but I did my best to answer properly here.
So if you could mark brainliest that would be awesome.
