Answer:
DE = 27
Explanation:
You have congruent triangles CDE and FGH with angle D = 2x-9 and angle G = x+17. The measure of GH is 79 -2x, and you want the measure of DE.
Corresponding measures
In congruent triangles, corresponding parts are congruent. Angles D and G are corresponding, so we have ...
∠D = ∠G
2x -9 = x +17
x = 26 . . . . . . . . add 9-x to both sides
Also, side DE is congruent to side GH:
DE = GH
DE = 79 -2x
DE = 79 -2(26) = 27
The length of DE is 27 units.