Orly uses 3 cups of raisins for every 10 cups of trail mix she makes. How many cups of trail mix will she make if she uses 12 cups of raisins?

If Orly uses 3 cups of raisins for every 10 cups of trail mix, she will make (12/3)*10 = <<(12/3)*10=40>>40 cups of trail mix if she uses 12 cups of raisins. Answer: \boxed{40}.