When a 9-Kbyte data file is transmitted using the asynchronous(or start-stop) communication protocol at a speed of 2,400 bps, what is the “overhead” (time spent on sending start, stop, and parity bits except data bits) in seconds? Here, a start bit is first sent, followed by eight data bits, no parity bit, and one stop bit, for each byte of the data file. 

a) 7.5 

b) 11.25 

c) 30 

d) 37.5