A plane drops a hamper of medical supplies from a height of 3680m during a practice run over the ocean. The plane's horizontal velocity was 136 m/s at the instant the hamper was dropped. The acceleration of gravity is 9.8m/s^2. What is the magnitude of the overall velocity of the hamper at the instant it strikes the surface of the ocean? Answer in units of m/s. Please help- I don't know where to start or what formla to use!