Explanation :
The height of the wave is defined as the elevation of the crest minus the elevation of the trough.
or
The wave height is defined as the twice of the amplitude.
It is given that the amplitude of the wave is 4 feet. The height of the wave is given as :
![H=2a](https://img.qammunity.org/2020/formulas/physics/middle-school/s89fiivtc4hmvf1w8udmxs80vj4pdw4e4g.png)
Where a is the amplitude of the wave.
So, H = 8 feet.
Hence, this is the required solution.