The recipe calls for I cup of water to be mixed with 6 cups of cake mix. How much water should be mixed with 21 cups of cake mix?

1/x=6/21

What you need to do is set it up as a proportion. 1 cup to 6 cups cake mix, x cups to 21 cups cake mix.

21/6 is 3.5

So 3.5 cups of water to 21 cups of cake mix (:

Hope this makes sense!

The recipe calls for 1 cup of water for every 6 cups of cake mix.

So, if you take 21 and divide it by 6, which is 3.5, that's how much water you should add (in cups).