Given that A=Set of letters in the word LISTEN and B=Set of letters in the word SILENT.
Note that L,I,S,T,E and N are letters common to both these words.
Thus,{L,I,S,T,E,N}={S,I,L,E,N,T}i.e.,the sets are equal as every element of A is an element of B and every element of B is an element of A.