Before we answer this question, let us first understand what alternate hypothesis is.
The alternative hypothesis is the hypothesis which is used in the hypothesis testing and this is opposite to the null hypothesis. This is the test hypothesis which is usually taken to be that the observations are the result of a real effect in an experiment.
In this case since what we want to set up is the statistical test to see if the waves are dying down, then this means we are trying to determine if the wave height are decreasing, so lesser than 16.4 feet. Therefore:
The alternative hypothesis would state (ANSWER)
Ha: μ less than 16.4 feet and P-value area is on the left of the mean.
While the null hypothesis is the opposite and would state
H0: mu equals 16.4 feet
