Is the data set approximately periodic? If so, what are its period and amplitude?

not periodic
periodic with a period of 4 and an amplitude of about 7.5
periodic with a period of 4 and an amplitude of about 10
periodic with a period of 3 and an amplitude of about 10

Fourth option: periodic with a period of 3 and an amplitude of about 10

Step-by-step explanation:

In the data, we can see that our values go from values around 30, to values around 10, and then it goes up again,

The period will be the distance between two points where we have the maximum value.

The first maximum, 30, is on day 2.

The second maximum,  28, is at day 5

Then the period is something around 5 - 2 = 3

The amplitude will be half the difference between the maximum and the minimum.

The maximum is around 30.

The minimum is around 10.

The amplitude is about:

A = (30 - 10)/2 = 20/2 = 10

Then the period is about 3 and the amplitude is about 10.

The correct option is the fourth one.