Consider a 32-bit microprocessor, with a 16-bit external data bus, driven by an 300 -MHz input clock. How many seconds you need to transfer 256 MB data? How many seconds you need to transfer 20 GB data if the bus is available only 35% of the time?
I think 2B because 2 bytes is 16 bits.
The combination of 16 bit external data bus and a 300MHz clock sounds fictional to me. I think that by the time busses ran on 300MHz clocks transfer rates already are measured in GB/s and multiple transfers per clock tick happened.
When 16 bit busses were used the transfer rate was 16MB/s on a 8MHz clock: https://www.cs.umd.edu/users/meesh/cmsc411/website/projects/buses/buses.html