We know that if sum of digits of a number is divisible by 9, then the number is divisible by 9.
Here,
x + 4 + y + 5 + z = multiple of 9
x + y + z + 9 = 0, 9, 18, ….
Hence,
x + y + z + 18 = 18
But x + y + z cannot be 0 because then x, y and z will have to be 0.Since x is the first digit, it cannot be 0.∴ x + y + z + 18 = 27
x + y + z = 9
∴ the least value of (x + y) is 9