#49, #50, #51, #52. The idea of these problems is to give you some practice constructing simple proofs. You can use the proof of Theorem 4.3 on p.181 as a model. The justification for each step can either be something like "associative property", "commutative property", etc., or can be a specific reference (e.g., "Theorem 4.2, part 4").
#1, #2, #5, #6, #7, #8, #11, #12, #15, #16, #19, #20, #21, #22.