Textbook Problem

One urn contains one blue ball (labeled $B_1$) and three red balls (labeled $R_{1,}{R}_2$ , and $R_3$). A second urn contains two red balls ( $R_4$and $R_5$ ) and two blue balls ( $B_2$ and $B_3$). An experiment is performed in which one of the two urns is chosen at random and then two balls are randomly chosen from it, one after the other without replacement.
a. Construct the possibility tree showing all possible outcomes of this experiment.
b. What is the total number of outcomes of this experiment?
c. What is the probability that two red balls are chosen?