There are 2 trees in a garden, A and B. Each tree has some birds on it. The birds of
tree A tell the birds of tree B that if one of them come to their tree, then their population will be
double that of tree B. Then the birds of tree B, tell the birds of tree 'A' that if one of them comes
to tree B, then their population will be equal to that of tree A. How many birds are there on each
tree?