We know that if sum of digits of a number is divisible by 9, then the number is divisible by 9.

Here,

x + 2 + 7 + y = multiple of 9

x + y + 9= 0, 9, 18, …

Hence,

x + y + 9 = 9

∴ x + y =0

But x + y cannot be 0 because then x and y both will have to be 0.
Since x is the first digit, it cannot be 0.
∴ x + y + 9 = 18

x + y = 9

∴ the least value of (x + y) is 9