Determine whether (-2, -4) is a solution to the system of equations: x - y = 3 and 8x - y = -4

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Ateacher wanted to buy a chair, a bookshelf, two tables and a desk. she spent $900 for all five items and the chair and the desk combined 70% of her total. if the bookshelf cost $50, how much did each of the tables cost?

Sole the equation 6n + 9 = -3n - 21 - 6 for n