Look at the duncan.txt (Duncan Hines brand) and betty.txt (Betty Crocker brand) files on 
the course web page.  Read these in as separate data sets (the variables in each file are 
Flavor and Height).  Be sure to also use a variable for cake brand.  

(a) Stack these two data sets with a SET statement, and print the new (combined) data set.

(b) Merge the two data sets by flavor, and print the new (combined) data set. Be sure the 
merged data set indicates which cake brand goes with which height.

(c) Use PROC MEANS to calculate the mean and standard deviation of heights, for each 
flavor, writing the summary statistics to an output data set.  
Merge these summary statistics with the stacked data set created in part (a) and print 
the resulting data set.