The correct answer is (i) and (ii). Both of the sets are subspaces of R3 because they satisfy the three criteria of a subspace. The first set, z = (x+y)2, is a set of all triplets (x,y,z) such that z = (x+y)2. The second set, x=10z, is a set of all triplets (x,y,z) such that x = 10z. Neither of the other choices are correct.