Why can we use trigonometric functions to describe periodic behavior, even when the behavior does not involve angles measured in radians or degrees?

The frequency table shows the results of a survey comparing the number of beach towels sold for full price and at a discount during each of the three summer months. the store owner converts the frequency table to a conditional relative frequency table by row. which value should he use for x? round to the nearest hundredth. 0.89 0.90 0.92 0.96