The diver was running in the horizontal direction. This means that the velocity, 3.6m/s is in the horizontal direction. This is known as Vx. The speed in the vertical direction, Vy is 0. The diagram representing the scenario is shown below
From the diagram, h represents the height of the cliff. We would find the height by applying the formula,
dy = vyot + 1/2ayt^2
dy is the displacement in the vertical direction and it is same as h
vyo is the velocity in the vertical direction and it is zero
a is the acceleration due to gravity
t is the time taken to to reach the height, h
From the information given, vyo = 0, t = 2.5, a = 9.8
By substituting these values, we have
dy = h = 0 * 2.5 + 1/2 x 9.8 x 2.5^2
h = 1/2 x 9.8 x 2.5^2
h = 30.63
The height of the cliff is 30.63 m