To calculate the required data rate, first calculate the total number of bits transferred per second.
- Each page has 1600 characters, and each character is 8 bits. Therefore, each page has:
\[
1600 \times 8 = 12800 \, \text{bits}
\]
- The user wants to upload 10 pages per 20 seconds, so the number of bits uploaded per second is:
\[
\frac{10 \times 12800}{20} = 6400 \, \text{bps}
\]
Therefore, the required data rate is 6400 bps, so the correct answer is "6400 bps."