A certain store sold pens for $0.35 each and pencils for $0.25 each. If a customer purchased both pens and pencils from the store for a total of $3.50, what total number of pens and pencils did the customer purchase?
Pick one: A) 8 B) 9 C) 10 D) 11 E) 12

Rationale: "answer : algebraically , the question looks like this : 2.5 = 0.35 x + 0.25 y there are six possible numbers of pens that fit that requirement : 1 pen : $ 0.35 2 pens : $ 0.70 3 pens : $ 1.05 4 pens : $ 1.40 5 pens : $ 1.75 balance can fetch 7 pencils for $ 0.25 each . that ' s 5 pens and 7 pencils for a total of 12 pens and pencils . choice ( e ) is correct ."
Answer: E