Are you clear on how to use vectors and components of trajectories? Whenever faced with a problem containing a vector, see if you can divide it into components pointing along the coordinate axis of a coordinate system that you are familiar with. In this case a cartesian is the given choice.
Once the components have been identified, answer these questions:
What vertical and horizontal speeds does the cannon ball have at the top of the trajectory?
At what time does it reach this point?
What horizontal and vertical speeds does it have when it hits the cliff?
How do you calculate the resultant speed from its components?