Expected amount of subsets:
Cardinality of Set B is 4, so 2^4 = 16.
Zero at a time: { }
One at a time: {M} ; {E} ; {N} ; {U}
Two at a time: {M, E} ; {M, N} ; {M,U} ; {E, N} ; {E, U} ; {N, U}
Three at a time: {M, E, N} ; {M, E, U} ; {M, N, U} ; {E, N, U}
Four at a time: {M, E, N, U}
Hope that helps...
