mccormick country gravy mix. Currently at work and have to serve 15 to 20 people for breakfast and I can't figure out how much mix and ingredients.

This looks like it will help. From Instacart page of info selling the Mccormick gravy:

Directions, 1. Stir water gradually into Gravy Mix with whisk in saucepan., 2. Stirring frequently, cook on medium heat until gravy comes to boil. Reduce heat and simmer 1 minute. (Gravy will thicken upon standing). Serve over biscuits, fried steak, fried chicken, home fries or sausage., For 2 cups of Country Gravy, mix 2/3 cup of gravy mix with 2 cups of cold water., For 1 quart of Country Gravy, mix 1-1/3 cup of gravy mix with 4 cups of cold water., For 1 gallon of Country Gravy, mix the full bottle of gravy mix with 14 to 16 cups* of cold water., *Use 14 cups of water for thicker gravy; 16 cups water for thinner gravy.
Warnings
Do not use if cap shrink-wrap is broken. Cook for food safety.

https://www.instacart.com/products/3073693-mccormick-original-country-gravy-mix-18-oz#:~:text=Serve%20over%20biscuits%2C%20fried%20steak,mix%20with%2014%20to%2016