Megan earns a rebate each month on completing surveys and books. She earns $0.75 for each survey she completes and $1 for each book. Last month Megan completed 8 surveys and earned $21.
Part A: Create an equation that will determine the number of books she purchased.
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B: Solve this equation justifying each step with an algebraic property of equality
Part C: How many books did Megan purchase last month?