Based on the given extended ratio 3:5:2, the amount of green paint Amber needs is 3x. She also needs 5x and 2x gallons of beige and white paints, respectively. These amounts of paints should add up to 35 gallons,
3x + 5x + 2x = 35 ; x = 3.5
The amount of white paints she needs is 2x which is (2)(3.5) and is equal to 7. Thus, Amber needs 7 gallons of white paint to paint the interior of her house.