I need help with this question

Which is an equation for the nth terms of the sequence 12,15,18,21

Analyze the data sets below. data set a 25,25,25,26,26,26,27,28,28,29,30,31 ,31,32,33,33,34,35,35,35 data set b 25,25,25,26,26,26,26,27,27,27,27,28 ,28,29,29,30,31,31,32,34 which of the following statement are true? select all that apply. a. data set a is relatively symmetric and data set b is skewed left. b. the means of the data sets are within 3 units from eachother. c. the data sets have the same standard deviation. d. the mean of data set a is 27.95 and the mean of data set b is 30. e. the data set b has a higher standard deviation than data set a. f. the mean and median of data set a are close in value.

Need on this one asap im almost done with this subject