The board is 2.50m high.
Why?
We can calculate how high was the board applying the Law of Conservation of Mechanical Energy. This Law states that the mechanical energy (kinematic and potential) will be conserved during the motion.
It can be described with the following formula:
At the top of the boar, the kinetic energy is equal to 0.
At the water, the potential energy is equal to 0.
So,
Hence, we have that the board is 2.50m high.
Have a nice day!