Answer:
5.59 times per second.
Explanation:
Direct variation is in the form:

Where k is the constant of variation.
Inverse variation is in the form:

In the given problem, the frequency of a vibrating guitar string varies inversely as its length. In other words, using f for frequency and l for length:

We can solve for the constant of variation. We know that the frequency f is 4.3 when the length is 0.65 meters long. Thus:

Solve for k:

So, our equation becomes:

Then when the length is 0.5 meters, the frequency will be:
