If ` 21 y8` is a multiple of 6, where y is a digit, what might be the value of `y` ?

Explanation

For the number `21y8` to be a multiple of `6`, it must be divisible by` 6`.
As per the rule for a number to be divisible `6`, it should be divisible by `2` and `3` both.
The above number is divisible by `2` because in the unit's place we have`8` which is divisible by `2`.
Next for the number to be divisible by `3`, the sum of all the numbers should be divisible by `3`.
`=> 2 + 1 + y + 8 = 11 + y` should be divisible by `3`
`=> y` can be only `1, 4, 7.`
Thus the value of `y` can be `1, 4, 7.`