SOLUTION
Statement1: Given a line segment 

Statement 2: Definition of Midpoint 
 D as the midpoint 
Then we have
Statement 3: Segment addition postulate 

Statement 4: simplify 

Statement 5: Addition property
Then Adding DE to both sides 

Then from the diagram,

We have 
Statement 6: Transitive property

statement 7: Division property
Divide both sides by 2

Therefore 
DE=1/2 CE implies D is the midpoint of CE
Statement 1= Given 
Statement2=Difine a midpoint 
Statement 3=Segment addition postulate
statement 4=simplify 
Statement5= Addition property
Statement 6=transitive property
Statement 7=Division property