DRDO Multi tasking staff Model paper 9

The logic here is as follows,
18!10 → 18 - 10 = 8, 8 ÷ 2 = 4
10!4 → 10 - 4 = 6, 6 ÷ 2 = 3
4!8 → 4 - 8 = -4, -4 ÷ 2 = -2
Similarly,
16!18 → 16 - 18 = -2, -2 ÷ 2 = -1
Thus 16!18 equals to -1.