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

Here,

x + 4 + 8 + y = multiple of 9

x + y + 12 = 0, 9, 18, ….

Hence,

x + 11 = 18

∴ x = 7

∴ the least value of x is 7