Sam celebrates a very special day today because he turns thirty-one years old. He feels very happy and wants to organize a small party inside his apartment tonight. He invites twelve guests to his house, including his best friends and his family members. Now, Sam is at a large local supermarket because he needs to buy some food. He looks at his wallet and discovers that he has exactly one hundred dollars. First, he chooses a big chocolate birthday cake, and the delicious sweet costs twenty-five dollars. Next, he buys twelve small sodas, and the box of drinks costs ten dollars. He also selects a modern box of plastic cups and napkins for five dollars. Finally, he buys fifteen delicious fresh pizzas, and they cost forty-five dollars in total. Sam calculates the total numbers in his mind and realizes that he has fifteen dollars left. He smiles because his budget is perfect, pays the cashier, and walks home happily.