How do you find the maximum height of a diver who jumps up of a diving board, with the initial speed of 8m/s. The diving board is already 5m high from the water. And the total time the diver is airborn is 2.115 sec.

Use the formula

s is the displacement,
v= your final velocity
u= your initial velocity
a= your acceleration

Have a sketch, this will help you assign positive values and negative values. I have to tell this because errors can arise if you don't take the directions into consideration. If you take the upward direction to be positive, then, the downward direction will always be negative.

Then, the initial velocity is positive, the displacement negative and the acceleration is also negative.

Then, to find the maximum height, solve for v = 0

To find the acceleration due to gravity, use
where t is the time during which your diver is airborne.

If you are stuck somewhere, post back :)