Daniel uses the proportions of cups of orange juice and cups of carrot juice to make a mixed juice.
Now, in the question 1 cup of carrot juice is used. So 4 times of the proportion of the carrot juice is used. Accordingly 4 times of the cups of orange juice will be used.
So what you would do, you would do as follows; you have a situation where is says "every week'' so you would put 17x=153. So to solve that, you would divide 153 by 17, and that's how you would get your answer of 9.