Use following properties:
X-Y=X∩Y'
(X∩Y)'=X'∪Y'
A-(B∩C)=A∩(B∩C)'=A∩(B'∪C')=(A∩B')∪(A∩C')=(A-B)∪(A-C)
Or use the basic definitions: if x is in then x is in A but not in . That, in turn, means it is either NOT in B or NOT in C.
case 1: x is in A but not in B. Then it is in .
case 2: x is in A but not in C. Then it is in .