If it is possible to make a number which is a perfect square of two-digit odd number with the second, the sixth and the ninth digits of the number 187642539, which of the following is the digit in the unit's place of that two-digit odd number ?
1) 1
2) 7
3) 9
4) No such number can be made
5) More than one such number can be made

Explanation

2, 17