2. [10 pts] Rohan's latest obsession is Trader Joe's, and he decides to map out the locations of the Trader Joe's stores in his city. He maps out a set of stores linked by roads (one road links exactly two stores) and he observes that on his map every store has exactly 7 roads linked to it. Prove that it is not possible for the total number of roads on Rohan's map to be 39