A $64-$bit processor has a cache with a capacity for $64$ Kilobytes $(1$ Kilobyte $=1024$ bytes$)$ of data. This excludes any additional bits used in the cache for tags, valid bits, dirty bits, or reference $($LRU bits$).$ The cache is four$-$way associative and has a block size of $64$ bytes. If the address bits are numbered from $0($least significant$)$ to $63($most significant$),$ what is the range of bits $($lowest$,$ highest$)$ that the processor uses to index a set in the cache? Low set index bit $\_,$ High set index bit $\_$