The subsets of a set are all sets within a set. So the subsets of Set U are:
{w}, {i}, {s}, {d}, {o}, {m}, {w,i}, {w,s}, {w,d}, {w,o}, {w,m}, {i,s} {i,d}, {i,o}, {i,m}, {s,d}, {s,o}, {s,m}, {d,o}, {d,m}, {o,m}, {w,i,s}, {w,i,d}, {w,i,o}, {w,i,m}, {w,s,d}, {w,s,o}, {w,s,m}, {w,d,o}, {w,d,m}, {w,o,m}, {i,s,d}, {i,s,o}, {i,s,m}, {i,d,o}, {i,d,m}, {i,o,m}, {s,d,o}, {s,d,m}, {s,o,m}, {d,o,m}, {w,i,s,d}, {w,i,s,o}, {w,i,s,m}, {w,i,d,o}, {w,i,d,m}, {w,i,o,m}, {w,s,d,o}, {w,s,d,m}, {w,s,o,m}, {w,d,o,m}, {i,s,d,o}, {i,s,d,m},{i,s,o,m} {i,d,o,m}, {s,d,o,m}, {w,i,s,d,o}, {w,i,s,d,m}, {w,i,s,o,m}, {w,i,d,o,m}, {w,s,d,o,m}, {i,s,d,o,m}, {w,i,s,d,o,m}, { }
There are 64 subsets, for any set with n number of terms there are 2 raised to n subsets since,
# of subsets of:
{ } - { } -1
{a} - { }, {a} - 2
{a,b} - {a}, {b}, {a,b} , { } -4