Understand serial and parallel transmission, synchronous and asynchronous transmission, bit rate, baud rate and bandwidth, and the trade-offs between these methods.

Bit rate $=$ baud rate $\times$ bits per symbol $= 4800 \times 3 = 14\,400$ bits per second.

The file is $9000$ bytes $= 9000 \times 8 = 72\,000$ bits.

Time $=$ bits $\div$ bit rate $= 72\,000 / 14\,400 = 5$ seconds.

Markers reward multiplying baud by bits per symbol for the bit rate (14 400 bps), converting bytes to bits, and dividing to get 5 seconds. A candidate who confuses baud and bit rate (using 4800) would get the wrong time and lose the method link.

Parallel transmission sends several bits at once down multiple wires, which is fast over short distances, but over longer distances the separate lines suffer from skew (bits travelling down slightly different-length or differently-affected wires arrive at slightly different times) and crosstalk (signals interfering between adjacent wires). These effects worsen as speed and distance increase, so the bits can no longer be reliably read together.

Serial transmission sends bits one after another down a single line, avoiding skew between lines, so it stays reliable at high speeds and over long distances, which is why modern high-speed links such as USB use serial transmission.

Markers reward identifying skew and crosstalk as the problems with parallel over distance and that serial avoids inter-line skew, making it reliable at high speed.