A discount bookstore sells hardcover books for $12 and paperback books for $6. The number of hardcover books, x, sold one day was twice the number of paperback books, y, sold the same day. The total sales that day were $180. What is the system of equations that represents this situation?

What is the next step in the given proof? choose the most logical approach. a. statement: m 1 + m 2 + 2(m 3) = 180° reason: angle addition b. statement: m 1 + m 3 = m 2 + m 3 reason: transitive property of equality c. statement: m 1 = m 2 reason: subtraction property of equality d. statement: m 1 + m 2 = m 2 + m 3 reason: substitution property of equality e. statement: 2(m 1) = m 2 + m 3 reason: substitution property of equality