In the DATA step provided, average is calculated using the mean function, which calculates the average of the non-missing values of the variables listed. The variables provided are: var1 = 2 var2 = 4 var3 = . var4 = 6 The mean function in SAS ignores missing values, represented by a period (.). Hence, the average is computed using the non-missing values (2, 4, and 6). The mean of these three numbers is calculated as: (2 + 4 + 6) / 3 = 12 / 3 = 4 Therefore, the value of average is 4. Reference: SAS documentation on the MEAN function, SAS Institute.