Suppose a byte$-$addressable computer using set associative cache has $2^21$ bytes of main memory and a cache of $64$ blocks, and each cache block contains $4$ bytes.

a$)$ If this cache is $2$ way set associative what is the format of a memory address as seen by the cache; that is$,$ what are the sizes of the tag, set, and offset fields?

b$)$ If this cache is $4$ way set associative $,$ what is the format of a memory address as seen by the cache?