Help please

In an alloy of 150 pounds of zinc and copper, there are 100 pounds of copper.     

How much copper must be added so that alloy may be 10% zinc??      

Since there are 100 lb copper, the other 50 lb are the zinc.     

You want that 50 lb to be 10% so the alloy must total 500 lb.     

There's already 100 lb copper so add another 350 lb copper.     

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