Have you ever seen an old western movie in which a cowboy would drink half a bottle of whiskey in the saloon and then walk out and have a successful gunfight? That was possible because the whiskey sold in the Wild West was generally 15\% alcohol. The wilder the saloon, the less alcohol was in the bottle. Everybody diluted a little more and more until the whiskey was hardly stronger than wine or tea. In the United States 100-proof whiskey means that the drink is \(50 \%\) alcohol. Suppose a bartender wishes to dilute a gallon of 100-proof whiskey to make it "a \(15 \%\) drink." How much water must be added?