One side have a total 9 seats, so 9 guests can be arranged on one side in $\ ^{9}P_{9}$ ways $= \lfloor 9$. Out of total 18,7 wish to be seated on particular sides. Remaining 11 can be seated in $\ ^{11}C_{5}$ ways. Since their are only 5 seats left after the 4 guests are seated on one side. So total no of ways required in which arrangements can be made $= \ ^{11}C_{5} \times 9! \times 9$