A contractor finds that 3 gallons of paint will cover 675 sq ft of wall area. How much wall area could be covered with 15 gallons of paint?
To determine how much wall area could be covered with 15 gallons of paint, divide the amount of wall area covered by 1 gallon of paint by the number of gallons of paint.
The amount of wall area covered by 1 gallon of paint is 675 sq ft.
15 gallons of paint can cover 15 * 675 = <<15*675=10125>>10,125 sq ft of wall area. Answer: \boxed{10,125}.