5) [20 marks total] Consider the statement: "My brother is left-handed, but if the key is not missing, then my brother is not left-handed; therefore, the key is missing." a. [10 marks] Assign letters to the basic propositions and write each hypothesis and the conclusion as an implication. b. [10 marks] Prove the correctness of your answer to item a. by using the logical equivalencies and/or rules of inferences tables from your text which are also available below