Let X be the number of energy drinks sold.
The manufacturer of an energy drink spends $1.20 to make each drink and sells them for two dollars the manufacturer also has fixed cost each month of $8000.
The manufacturing cost for X energy drinks is

Fixed cost is $8000.
Therefore, cost function is

Selling price of each drink is $2.
Therefore, the revenue function is

Hence, the revenue function is
3 feet, you divide 81 by 9 and you get the square feet of the pantry, then you divide that by 3
One decade is 10 years+ 8 years is 18 total years
18 minus 9 is 9 years
Hope this helps
This is what i got when i worked it out