Finding the Period of a Sinusoidal Model for Ice Cream Sales

[mathuravasant]

The owner of an ice cream shop kept records of the average number of sales per month for 2019. Create a sinusoidal equation to model this information of number of sales per month.I found the maximum, minimum for this, but how can I find the period of from this table.
As I already know formula to find period is =2pi/k but how can I find K-value from this chart??

 

[topsquark]

Hint: Looks to me like the time span between January and November is the first 1/2 of a sine wave, doesn't it?

-Dan