Michael W. answered 10/02/19
SW Engineer w/ MS CompSci & BS Math
Px = Probability Tx wins at Fx (Tx Team X and Fx Field X)
Py = Prob Ty wins at Fy =0.7
Scenario 2: Py is in play, so Px = 0.3
Scenario 1: Probability of X champions is Px^2 because they have to win twice.
So for scenario 1 to be better than 0.3, Px must be greater than the square root of 0.3.
Since you have 4 answer options. Square the lower limit of each. You'll find that only one results with a value greater than 0.3. That is your answer.