Answer:
C = 9 centimeters
Explanation:
First, look at the area of a square, which formula is c^2 or in standard format - s^2. Thus, we can say, c^2 = 81. Then, we can simplify, and put c = √81. Since 81 is a perfect square, 9 * 9 = 81. Thus the answer is 9 centimeters.