Draw any point, call it X
Construct the parallel to AB through X
Construct the parallel to AX through B
Call the meet of the two parallels Y
Conclude XY ≡ AB
There are a few different ways of constructing parallels; look those up if need be.
I'll write the 1D coordinates in the form (x)
2. D = (0)
3. C = (2)
4. E = (3.5)
5. BE = -3.5 - -4 = 0.5
6. DB = 0 - -4 = 4
7. EC = 2 - -3.5 = 5.5