How much cake mix does it take to fill number 21?

It's impossible to say how much cake mix it takes to fill the number "21" without knowing:

* The size of the number 21: Is it a tiny number 21 made from cookie cutters, a large 21 made from cardboard, or something in between?

* The shape of the number 21: Is it a flat, two-dimensional cutout, or a three-dimensional model?

* The density of the cake mix: How much air is incorporated into the batter? This will affect how much cake mix fits into the mold.

To figure out how much cake mix you need, you'll need to determine the volume of the mold for the number 21.

Here are some helpful steps:

1. Measure the mold: If you have a physical mold, measure its length, width, and depth.

2. Calculate the volume: Multiply the length, width, and depth to get the volume in cubic units (e.g., cubic inches or cubic centimeters).

3. Consider cake batter expansion: Cake batter will rise as it bakes. Add some extra volume to your calculated volume to account for this.

Once you know the volume of the mold, you can use a standard cake mix recipe to estimate how much mix you need.