(a) Since the probability distribution is uniform in the square K(take it as ABCD here), there P(ξ,η) = 1 for all points inside the square(why? : because ∫∫P(ξ,η)dξdη with 0<ξ<1 & 0<η<1 should be 1 and marginal distribution for ξ and η are uniform)
Now we need to find probability of all those...