What is the value of x so that the seven digit number 8439x53 is divisible by 99?

8439x53 will be divisible by 99 if it is divisible by both 9 and 11.

Rule for 9:A number is divisible by 9 if the sum of the digits is divisible by 9

Rule for 11:Subtract and then add the digits in an alternating pattern from left to right. If the answer is 0 or 11, then the result is divisible by 11

If x= 4 , then sum would be 36, satisfying the rule for 9.

Now , check for 11 : 8 - 4 + 3 - 9 + 4 - 5 + 3 = 0

So , the answer would be option b)4.