here my answer
The device generates 8 × 1024 = 8192 bytes per second or a rate of one every 122 µs. If each interrupt consumes 100 µs, then the fraction of processor time consumed is 100/122 = 0.82The device generate 8*1024 bytes or rate of one every 122 us If interrupt is 75us, then the fraction of processor time will be 75/122 = 0.61
thus it should be c as that's the closest