If one gallon of paint overs 825 sq. ft how much paint is needed to cover 2640 st. ft

If 1 gallon covers 825 sq ft then look at this:

825 times 3 gallons would cover 2,475 sq ft

825 times 4 gallons would cover 3,300 sq ft

You would need the 4 gallons to cover because 3 gallons wouldn't be enough