Let the radius of the circular pond be x.
The pictorial representation of the problem is given below:
Recall the Tangent to a Circle Theorem:
It follows that we have a right triangle as shown:
Hence, the right triangle has legs with lengths 78 and x, and a hypothenuse of length 41+x.
Use the Pythagorean Theorem:
Solve the resulting equation for the radius x:
Hence, the required radius of the pond is about 54 ft. to the nearest integer.