Given speed of the device = 16 KBps
So in 1 s , data transferred = 16 KB
So time taken to transmit 1 byte = 1 / (16 * 210) s
= 61.035 μs
Given interrupt overhead for each byte transfer = 50 μs
So fraction of processor time involved = Time of interrupt overhead / Total time
= 50 / 111.035
= 0.450
Hence 0.450 should be correct answer..