Consider an urn in which 4 balls have been placed by the following scheme. A fair coin is tossed; if the coin falls heads, a white ball is placed in the urn, and if the coin falls tails, a red ball is placed in the urn. (i) What is the probability that the urn will contain exactly 3 white balls? (ii) What is the probability that the urn will contain exactly 3 white balls, given that the first ball placed in the urn was white?