It states that “a number divisible by 9 should have the sum of its digits equal to a multiple of 9”.

Now, here in this question we know that 24x is divisible by 9. So, the relation between the digits and multiple of 9 will be:

Letmmbe a factor of the multiple of 9.

2+4+x=9m2+4+x=9m

6+x=9m6+x=9m

6+x9=m6+x9=m

This is here an equation in two variables. So it should have infinite solutions. But sincexxis a digit,xxcould neither be negative nor could be more than 9. Andmmcould only be a natural whole number because the sum of digits of a number could never be negative and in this case it couldn't even be zero because if any of the numbers in an equation of addition is a natural number then the sum should also be a natural number.

Therefore, we should have the values ofxxbetween the range 1–9.

We should find it by trial and error method. I can't try them all here, so I am giving you the answer to it now.

The only possible value forxxwhich would satisfy the situations is 3.

Therefore,x=3x=3.