To simplify the number 6443, we can look for an appropriate representation such as rounding or conversion if it's necessary. However, none of the options provided (4096, 256, 85.3, 16) seem to relate directly to a mathematical simplification or approximation of 6443 without context.
If this is looking for the nearest simplification in terms of powers of 2, 4096 (which is \(2^{12}\)) is the closest, as it is less than 6443.
If you have context for how 6443 needs to be simplified (e.g., rounding, approximating, or another method), please provide that for a more accurate simplification.
Based on the information given and the options provided, the best response could be 4096.