(a)[4]
Since the particle is above the level of the top of the building for $4\,\text{s}$, determine $h$.
(b)[4]
A second particle is projected vertically upwards from the top of the building with speed $20\,\text{m s}^{-1}$, 1 second after the first particle is projected. If $t\,\text{s}$ is the time measured from the first projection, determine the value of $t$ when the two particles are at the same height above the ground.