A certain alloy contains 14% tin and 32% copper. (The percentages are by weight.) How many pounds of tin and how many pounds of copper must be melted with 1750 lb of the given alloy to yield a new alloy containing 20% tin and 35% copper? Hint: Introduce variables for the weights of tin and copper to be added to the given alloy. Express the total weight of the new alloy in terms of these variables. The total weight of tin in the new alloy can be computed two ways, giving one equation. Computing the total weight of copper similarly gives a second equation.