As I am new in this plz can some one help me to simplify this expression ,i try but i am not sure is it corect or wrong.

expression is

F=A'.B'(A.B+B')

F=A'.B'(AB+B')

F=A'.B'(A+B+B') BY USING DEMORGAN LAW

F=A'.B'(A+(B+B')) By rearranging above expression

F=A'.B'(A+1) BY USING RULE#11

F=A'.B' BY USING RULE #5

F=(A+B)'