It takes 5 dogs 6 days to eat 90 cups of food. how many days will it take 8 similar sized dogs to eat 150 cups of food? a) 2.5 days b) 4.8 days c) 5.5 days d) 6.25 days

So if it takes 5 dogs 6days to eat 90 cups of food, then we can conclude that it takes 1 dog 6 days to eat 18 cups of food (90/5). From here we can say that it will take 1 dog 1 day to eat 3 cups of food (18/6). 

Now it says we have 8 similar sized dogs, so we can conclude that it will take 8 dogs 1 day to eat 24 cups of food (3 x 8). Now we need to find how many days it'll take to eat 150 cups, so we just do a simple division to find it:
150/24 = 6.25
So your answer is 6.25 days, D