4A3+984=13B7
We can observe that A and B are single digits .so, they must lie between [0,9]
Now, since it is divisible by 11 it must follow divisibility rule of 11
which is, The alternative sum of the digits of Number is divisible by 11
⇒1−3+B−7 is to be divisible by 11 or 1−3+B−7=11α
Also, 13B7 can also be written as 11α where α is any integer
here, since B can only lie between [0,9], only value of α satisfying 1−3+B−7=11α is 0
⇒1−3+B−7=0⇒B=9
Also, B=A+8⇒9=A+8⇒A=1
Therefore, A=1,B=9
So. A+B=10