Isabella has three times as many green houses as yellow houses. She also has 40 fewer yellow houses than red houses. If she has 90 green houses, how many of her houses are not yellow? Let's answer step by step:
If the number of green houses is three times the number of yellow houses, and there are 90 green houses, then there are 90 / 3 = 30 yellow houses. She also has 40 fewer yellow houses than blue houses, meaning there are 30 + 40 = 70 blue houses. The number of houses that are not yellow is 70 blue houses + 90 green houses = 160. The answer: 160.