Combine multiple rows in a specific column based on matching criteria? VBA solution?

I am hoping for some VBA wizardry. I have 2 columns of data that need help. The first column (A) is the CRN # that identifies the class. The other column (D) “Class Days” shows the days of the week for that class. Sometimes a class can have multiple rows. I am looking for a macro that can look at the CRN in column A and if there are multiple rows, then combine all the class days.
The code for each day of the week are as follows:
MON=M
TUE=T
WED=W
THU=R
FRI=F
SAT=S
SUN=U
The order is M T W R F S U
For example CRN # 20808 has two rows. In the first row, column d, “class days” says T. Then the second row says TR. Is it possible for multiple rows to have the exact same data in the “class days” column? The final result would show in column d, “TR” for both rows. Is it also possible for the cells in column D to be in order of the days of the week?
I have a sample attached. The master sheet contains all the data. The example sheet just shows the specific class I referenced above with the desired result.

I appreciate your help!
201620 Class Master Filter Final.xlsm

I will check this first thing tomorrow...thank you for such a quick response! I appreciate your help so much!