In 1s CPU makes 300 million ticks, so time for a tick (clock time) is 1/(300 * 106 ) = 3.3 ns.
For 900 cycles, CPU time will be 900*3.3 = 2970 ns = 2.97µs
Now, time for data transfer = 200/5000s = 40ms = 40000 µs
So, percentage of CPU time for transfer = 2.97/(40000+ 2.97) = 0.0074%