Let x be the length of one piece and y be the length of the other piece. Then, we can write:

since one piece must be twice long than the other, we can write

and we have 2 equations in 2 unknows.
Solving by substitution method.
By substituting equation B into equation A, we get

which gives

Now, in order to obtain y, we must substitute this result into equation B. It yields

Therefore, the answer is x= 20 inches and y= 40 inches.