Write the missing reasons. Assume that each variable represents any real number. Prove: (a + b) + (-b) = a
Proof:
1. a + b is a real number
2. -b is a real number
3. (a + b) + (-b) = a + [b + (-b)]
4. (a + b) + (-b) = a + 0
5. (a + b) + (-b) = a

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