ANSWER
0.68 m
Step-by-step explanation
The BMX rider leaves the end of the ledge with an initial velocity - which is horizontal, of 25m/s and travels a horizontal distance of 9.3 m until he lands,
In this type of motion, there is no horizontal acceleration so the horizontal velocity is constant, thus the horizontal displacement is,
From this equation, we can find how long the biker was in the air,
Now we can use this time to find the height of the ledge. The vertical displacement is,
The initial vertical velocity is zero because the biker left the ledge horizontally. g is the acceleration due to gravity, 9.81 m/s²,
The ledge is 0.68 m high.