help me pls...

PHYSIC-KINEMATICS
1.A ball is thrown horizontally from the roof of a building 45.0 m tall and lands 24.0 m from the base. What was the ball’s initial speed?

2. A ball thrown horizontally at from the roof of a building lands 36.0 m from the base of the building. How tall is the building?

how la dei... how to find speed when time isn't given.
i think it's something to do with free fall. hence acceleration is constant. hence u can use da formulas of situation with uniform acceleration.
a=9.8m/ss
x=45-24?=21? correct?
then wat's t?
haiyo. help. please