The I/O device generates $8*1024=8192$ bytes per second (or equivalently, 8192 bytes per 1000 ms). This means, one byte is generated every $\frac{1000}{8192}\approx 0.122$ms. CPU is busy for 100 ms once in every 0.122 ms. So fraction of time busy is given by: $\frac{100}{0.122}=819.68$
NB: Do you really mean $100$ms or 100$\mu$s? If it is 100$\mu$s, then answer would be $\frac{100}{122}=0.81968$. Approximately, 82% of processor time.
CPU is blocked during this time. So the same percentage of time, CPU remains in blocked state.