Answer:
The width of bookcase D is 61 cm
The width of bookcase E is 61 cm
Explanation:
see the attached figure to better understand the problem
step 1
Sum the widths of the three bookcases A, B and C

step 2
Subtract the sum of the three bookcases A,B and C from the total length of the wall

step 3
Divide that answer in step 2 by 2, and that will let you know the widths of D and E, because they may have equal widths

therefore
The width of bookcase D is 61 cm
The width of bookcase E is 61 cm