EX :1)
A = { 5,{5} } B = {5}
B "belongs to" A as element,{5} is present in A.
B "is a subset of" A as all elements of set B is present in all elements of A.
EX : 2)
A = {} and B = {{}}.
A "belongs to" B as element {} is present in B.
A "is a subset of" B as empty set is a subset of every set.