The answer is clearly C or E. Using both Statements, Daisy bought twice as many books and twice as many pens as Rosy. So if we think of books and pens as a single thing, let's call it 'supplies', Daisy spent twice as much on supplies as Rosy. Daisy also bought 1.2 times as many pencils as Rosy, so spent 1.2 times as much on pencils. Overall, she spent 1.5 times as much as Rosy. So we now have a weighted average situation, with two groups, one with an average of 1.2, and the other with an average of 2, and an overall average of 1.5. If you know the alligation method, you really don't need to do anything more - it's clear we can answer the question. If one wanted to solve, we can draw a number line:
---1.2-------1.5------------2---
and since the ratio of the distances to the average in the middle is 3 to 5, that's the ratio of the two groups. Since Rosy must have spent more on pencils (since 1.5 is closer to 1.2 than to 2), then 5/8 of her expense was on pencils. I'm using alligation here, and if that method is unfamiliar to anyone reading, this solution might not make a lot of sense, but you can find an explanation of the method by googling the term.
You could also solve algebraically: if Rosy spends $b on books and pens combined, then Daisy spends $2b on those things. If Rosy spends $p on pencils, then Daisy spends $1.2p on pencils. We know Daisy's overall expenditure is 1.5 times that of Rosy, so we'd get this equation:
2b + 1.2p = 1.5(b + p)
which can be solved for the ratio of b to p, from which we can answer the question.