36. Walter and Brian each have a CD collection.
The number of CDs in Walter's collection can be represented by x.
The number of CDs in Brian's collection is 3 times the number in
Walter's collection.
The total number of CDs in both collections is 144.
What is x, the number of CDs in Walter's collection?
A. 108
B. 48
C. 72
D. 36