Eight. That's because if we multiply 8 by itself, the result is 64. Taking the square root of a number means finding the number that when multiplied by itself returns the original number.
In the case of the number 64, because its square root is a whole number, 64 is called a perfect square number. This is because it can be represented by arranging 64 items into a square with a side length of 8 items. Read more