To find the circumference of a circle you have to multiple the radius by 2 and also by pi. So, to find the radius when given just the circumference, who have to do the reverse operation and divide the circumference by 2 and also by pi to get the answer of 22.92993631, which you could of course round.
The new coordinates are (3, 1)
I am pretty sure it is linear decrease,
Answer: Exponential table