The sum of the digits of a certain two-digit number equals the square root of the number?

4*4=16,1+6=7

5*5=25,2+5=7

6*6=36,3+6=9

7*7=49,4+9=13

8*8=64,6+4=10

9*9=81,8+1=9 so 9 square is 81 sum of these two digit is 9. 9 square is answer.