9 would be answer. when you plug in the 9 to the equation you get 14=14 which is a true statement.
The domain of a function are the possible input values of the function.
<em>The domain of the function is (d) Whole numbers</em>
First, we identify the start and end values of x on the graph.
We have:

The graph has no end; so:

This means that the domain of the graph is 
The number of times one can visit the pool cannot be decimal.
Hence, the domain of the function is whole numbers
Read more about domain at:
brainly.com/question/15339465