x=lenght of the middle sized piece.
2x=lenght of the longest piece.
x-10=lenth of the sohtest piece.
we can suggest this equation:
(2x)+(x)+(x-10)=70
4x-10=70
4x=70+10
4x=80
x=80/4
x=20
therefore:
lenght of the middle sized piece: x=20
lenght of the longest piece: 2x=2(20)=40
lenth of the sohtest piece: x-10=20-10=10.
Answer: the length of the longest piece is 40 in.