The probability of even a is x, and the probability of even b is y, if the two evens are independent, which of these conditions must be true?

I think you meant to write "event" instead of "even".

P(A) = x

P(B) = y

P(A and B) = P(A)*P(B)

P(A and B) = x*y

you multiply the two probability values. This rule only works because the two events are independent.

you can't solve x because it is 2 linear equation and you only have one equation

answer: yes, since the line has a steeper rate of change than the exponential the y-values will be greater and they will only intersect one time.