Answer:
The perimeter is c. 28 millimeters
Explanation:
The Perimeter of a Square
The perimeter of a square is the sum of all its side lengths. If the side length is L, then the perimeter is:
P = 4L
The diagonal of a square is the hypotenuse of a right triangle with both legs of length L.
Applying Pythagora's theorem, we find the length of the diagonal is:

We know the diagonal of a square is

We can find the side length L:

Simplifying:
L = 7 millimeters
Thus, the perimeter is:
P = 4*7 = 28
The perimeter is c. 28 millimeters