Answer:
Givens
and 
Points D, R, P and T are collinear.
The image attached shows a representation of this problem.
By sum of segments, we have

Replacing all given values, we have

Therefore, the segment DT is 10 centimeters long.
Now, we know that point E is the center of segment RP, which means is a middle point, divides the segment equally. So, to prove that segment DT is symmetrical regarding point E, we need to prove that both sides are equal.
, by definition of middle point.
By sum of segments, we have

Which means
.
Therefore, segment DT is symmetrical regarding point E.