subsets of P:
{ }
--------
{a}
{w}
{{k}}
--------
{a, w}
{a, {k}}
{w, {k}}
--------
{a,w,{k}}
{ } is the empty set.
There are 8 subsets. It is not coincidental that 2^3 = 8 and there are 3 terms in set P. Be careful about how you deal with the {k}. It is not simply the element k. It is a set within a set.