Final answer:
The radius of the circle created by the sprinkler is 15 feet.
Step-by-step explanation:
The area of the circle created by the water from the sprinkler is equal to the area of the square garden. Since the circle is inscribed in the square, the diameter of the circle is equal to the length of the side of the square. The radius of the circle is half the length of the side of the square, so in this case, the radius of the circle is 15 feet.