LOS 8E- Total Probability terms, events, someone, reading, understand

cmacedo

Can someone help make sense of this for me? I understand what an unconditional probability, a conditional probability, and mutually exclusive and collectively exhaustive events are, but I don't understand how you can have an unconditional probability of an event in terms of conditional probabilities...?? I may be reading to much into this but could someone lend a hand?

Thanks!!