By solving we get,
400*A + A*B = 10881
By trial and error method
We get B = 3
And A = 27
So
A +B = 30
But its just an assumption ,because in question its not mention that A + B must be an positive integer or something.
If the questions says that it must be an positive integer then a = 27 and b = 3 and a = 1 and b = 10481 can be the answer
