The correct option is D 128
Observing closely, we can see that the number filled in each rectangular block is the product of the numbers written on its circular neighbouring blocks.
13 × 6 = 78
6 × 4 = 24
4 × 16 = 64
8 × 8 = 64
4 × 13 = 104
So, 16 × 8 = 128.