Caylan is making baked goods for a charity bake sale. He places a tray of scones, a tray of muffins, and a tray of cookies in the oven. The scones bake for 15 minutes, the muffins bake for 12 minutes, and the cookies bake for 10 minutes. When one tray is done, he removes it and replaces it with another tray of the same item. What is the total baking time for the scones if Caylan continues to replace the tray with the same item each time it's done baking?
a) 15 minutes
b) 30 minutes
c) 45 minutes
d) 60 minutes