A 0.45 kg rock is projected from the edge of
the top of a building with an initial velocity of
9.9 m/s at an angle 56 ◦
above the horizontal.
Due to gravity, the rock strikes the ground at
a horizontal distance of 14.9 m from the base
of the building.
Is there a question in there somewhere?
Use your basic equations of motion to set things up.
When you are just starting out, you haven't yet learned very many rules. So, whatever problems you are given will use one of a very small set of rules to choose from. Learn those basics.
Wikipedia has a very nice article on Trajectories.
It will answer any basic problems you are given.