Please help me prove the following about the measure of the symmetric difference of sets

Let ( * , `, Me ) be a measure space . Prove the following : ( a) If { , F E.M and M ( FAF ) = 0 then u ( E ) = M ( F ). ( b ) Define E ~ { if and only if u ( EAF ) = O; then ~ is an equivalence relation on MM . ( c ) For E , F E / define d ( E , F ) = M ( LEAF" ) . Then a defines a metric on the set of equivalence classes MM / ~