Answer: DE = 79
Concept:
Here, we need to know the idea of segment addition postulate.
The Segment Addition Postulate states that given 2 points A and C, a third point B lies on the line segment AC if and only if the distances between the points satisfy the equation AB + BC = AC.
If you are still confused, you may refer to the attachment below for a graphical explanation or tell me.
Solve:
**Disclaimer** I assume that points D, E, F are collinear, thus they would form a segment and F would be the point between D and E. If it was, you may refer to my answers. If it was not, you may tell me and I will redo it.
Given information
DF = 61
EF = 18
Given expression deducted from the segment addition postulate
DE = DF + EF
Substitute values into the expression
DE = (61) + (18)
Simplify by addition
Hope this helps!! :)
Please let me know if you have any questions