E.g. 64, 144, 484 all are Perfect Square having the unit digit 4 and the tens digit is even. E.g. 25, 225, 625,1225 all are Perfect Square having the unit digit 5 and the tens digit is 2. – If unit digit of a perfect square is 6 then ten's digit has to be Odd.
What 2-digit number is the square of its units digit? You know the number is a two-digit and has to be the square of a 1 digit number, so there are six possible numbers.16, 25, 36, 49, 64, and 81 all other squares of one digit numbers are 1 digit numbers.