Level pending

Credit to Wee Xian Bin for the original problem.

Mark and Jolene are at it again. This time they are playing the badminton match such that whoever has 2 more set wins than the opposite player wins the game. If Mark still has a $$0.4$$ chance of winning a set, then the probability that Jolene will win the entire match can be represented as $$\dfrac{a}{b}$$ for coprime positive integers $$a,b$$. What is $$a+b$$?

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