I tried to simplify it as much as I could. Its my first week in this course and it's mind breaking. Here is what I got. If I have done it wrong can you please reply and let me know where I am wrong at? Thank you so much!

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(A - B) U A = (Ᾱ U B) U A = (Ᾱ∩A) U B = Ø U B = B

so my answer is that

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(A-B) U A= B