Mary is baking a cake. The recipe calls for 34 cups of sugar and 49 cups of flour. She already put in 13 cups of sugar. How many more cups of sugar does she need to add?
1. Mary is baking a cake. 
2. The recipe calls for 34 cups of sugar and 49 cups of flour. 
3. She already put in 13 cups of sugar. 
4. How many more cups of sugar does she need to add?

To solve this problem, we need to find out how many cups of sugar are in the recipe. We can do this by subtracting the amount of sugar Mary has already put in from the total amount of sugar in the recipe. 

34 cups of sugar - 13 cups of sugar = 21 cups of sugar

So Mary needs to add 21 more cups of sugar to the cake.