Answer:
13.8 feet long.
Step-by-step explanation:
The end two pieces are 3.6 feet long.
The middle board must be 0.82 longer than the 3.6 feet.
The easy way to do this is to realize that the length of the middle part is 1.82 times the length of each of the end pieces.
1.82 * 3.6 = 6.552 feet long.
So the total length of the board must be
3.6 + 3.6 + 6.552 = 13.752 feet long. (That's a pretty long board).
Rounded it becomes 13.8 feet long.
