The first question below has been answered, so I won't say it. His answer is right (copy, 35+65-20=80 (draw Wayne diagram, just two circles intersect)).

Question 2: a+ 1 =3, A+2A-3 = A+3, the solution is A = 2；; Or a+ 1 = a+2a-3, a+3=3, and a has no solution. So the final answer is a=2.

Question 3: x=4- 1=3 or 4-2 = 2 or 4-3 = 1 or 5- 1 = 4 or 5-2 = 3 or 5-3 = 2 or 6-65433.

I hope you are satisfied with my answer.