To determine how many gallons of red paint Bobby should buy, we need to calculate the total area of the west side of the barn and then divide it by the coverage of one gallon of paint.
The area of the west side of the barn is calculated by multiplying the length and width:
Area = Length × Width
Area = 20 feet × 75 feet = 1500 square feet
Since each gallon of paint can cover 300 square feet, we can now calculate the number of gallons needed:
Number of gallons = Area / Coverage
Number of gallons = 1500 square feet / 300 square feet/gallon = 5 gallons
Bobby should buy approximately 5 gallons of red paint to adequately cover the west side of his family's barn.