Answer:
One piece is 26 inches long while the other is 52 inches long.
We let:
x = one piece of the thread
2x = the other piece of the thread
Since the thread is 78 inches long,
2x + x = 78
Solve for x:


Since one piece of the thread is 26 inches long, the other piece would be:

The other piece would be 52 inches long.