Answer:
3
Explanation:
Hello!
A simple way to find if the number is a multiple of 9 is if the sum of the digits in the number is a multiple of 9, then the number itself is a multiple of 9.
So that means: 7 + 2 + b + 3 + 8 + 4 is a multiple of 9
If we add it up we should get: 24 + b
The multiples of 9 include 9,18,27,36,45,54....., and the closest multiple of 9 to 24 is 27. Therefore, the missing digit should be 3, as 27 - 24 is 3.
The next closest numbers would be 18 and 36, but you would need to add a negative number to get 18, and a two-digit number to get 36.