How to construct a Red-Black tree representing K in O(lg n)

Question

Suppose that K1 and K2 are sets of keys, and k is a key such that for any k1 ∈ K1 and k2 ∈ K2 we have k1 < k < k2. Let K = K1 ⋃ {k} ⋃ K2. Assuming that K1 and K2 are repre