A gave 6 pieces from his cake and took 5 pieces from B own + 3 from his own = so he got 8 pieces from all the cake so he pay for three cake 9 pieces

B gave 10 pieces from here cake and took 3 pieces from A own + 5 from her cake = so she took same 8 pieces from all cake but she pay for five cake 15 pieces

A PAY FOR 9 PIECES AND GOT 8 PIECES ----> 9-8 = 1
one PIECE HE GAVE FROM THE HIS SHARE

B PAY FOR 15 PIECS ABD GIT 8 PIECES -----> 15-8= 7
Seven PIECES SHE GAVE FROM HER SHARE

SO A will take only 1 for his one piece
And B will take 7 for her pieces