The question seems to be asking for a numerical simplification of the number 6443, but the options provided don’t directly correlate to any standard mathematical processes (like rounding, factoring, or finding a square/cubic root).
If we consider certain forms of simplification (like factoring or significant digits), none of the answers given (16, 4,096, 85.3, or 256) are direct simplifications of 6443.
If you are asking for a mathematical operation or specific type of simplification, please provide additional context. However, none of the offered answers appear to simplify or relate to 6443 in a conventional manner.