Final answer:
To enclose a dog pen with an area of 64 square feet, you will need 32 feet of chain fence.
Step-by-step explanation:
To find the length of the chain fence necessary to enclose a square dog pen with an area of 64 square feet, you first need to find the length of one side of the square.
Since the area of a square is calculated by multiplying the length of one side by itself, you can take the square root of 64 to find the length of one side.
The square root of 64 is 8, so each side of the square is 8 feet. Since there are four sides in a square, you need a total of 4 multiplied by 8, which is 32 feet, of chain fence to enclose the dog pen.