First find the number of gallons of blue paint by multiplying the gallons of green paint by the ratio between the blue and green paint: 1 blue gallon/2 green gallons * 6 gallons = 3 gallons
Then find the number of gallons of white paint by multiplying the gallons of green paint by the ratio between the white and green paint: 5 white gallons/2 green gallons * 6 gallons = 15 gallons
Then add the number of gallons of each color to find the total number of gallons of paint: 6 gallons + 3 gallons + 15 gallons = <<6+3+15=24>>24 gallons
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