A plane drops a hamper of medical supplies from a height of 4660 m during a practice run over the ocean. The plane's horizontal velocity was 121 m/s at the instant the hamper was dropped. The acceleration of gravity is 9.8 m/s/s. What is the magnitude of the overall velocity of the hamper at the instant it strikes the surface of the ocean?

Time taken for the hamper to travel 4660m in free fall is :

t=\sqrt{\frac{2h}{g}}

Using this value of t you can calculate the horizontal component of the velocity at the instant the hamper touches ocean :

v_y = gt

Assuming that drag/friction of air is zero, we already know v_x=121ms^-1

So the overall velocity is :

v=\sqrt{v_x^2+v_y^2}

That's it, done :)
Hope this helps.