I need to use 3 white cake mixes for a 14 X 20 cake pan. First one I baked came out to moist and broke up. Any suggestions on how to fix problem??? Lost my note on how to solve this problem. Know I have to alter ingred. but can't remember what and how.

After you mix the batter per box instructions, try adding 1 cup of flour per box mix (in this case you will be using 3 cups of flour) to the batter. Mix on low speed just until combined and bake as usual. The result is a moist yet sturdy cake.