Working with natural numbers and divisibility.

The natural number 28A9B consists of different numbers and A is not equal to 0. When the number is divided by 9 the remainder is 7 and when it is divided by 5, the remainder is 1. What is A-B=?

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... 9, the sum of all digit numbers should be a multiple of 9.
So to have a 7 remainder the sum should be 7,16,25,34,43....

So for B=1, we have,

2+8+A+9+1= 25 (possible ...