The experimental probability is, as the name suggests, a probability based on observation. If we say that the experimental probability of seeing a hawk at the Avian Viewing Center on any given day is 20%, it means that someone has visited the center for many days, and at the end of this experiment he has met hawks on 20% of the days, i.e. one out of five days.
If we assume that these measurement are trustworthy, we can assume that Allison will also see a hawk on one fifth of the days.
Since she will visit the center for 240, she should expect to see a hawk on one fifth of these days, i.e.
days.