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9-15.

Joanne was making repairs to her deck and needed to buy some supplies. She purchased two posts, three boards, and four piers for $52. When she needed more materials, she went back to the lumberyard and bought one post and five boards for $13. Realizing she did not need the piers, she made a third trip in which she bought three more boards, returned the four piers, and ended up with a refund of $34. What was the cost of each item? Homework Help ✎

Define variables for the number of posts, boards, and piers.

Write three equations with the three unknowns.

First Equation:
If x = # of posts; y = # of boards; z = # of piers, then 2x + 3y + 4z = 52.

Solve.