Answer:
The length and width of the deck will be 11 meters and 9 meters respectively.
Explanation:
The length of the rectangular deck is
meter and width is
meter.
The perimeter of the deck should be 40 meters. So, the first equation will be...

The difference between twice the length and twice the width should be 4 meters. So, the second equation will be....

Adding equation (1) and (2), we will get.....

Now plugging this
into equation (1), we will get....

So, the length and width of the deck will be 11 meters and 9 meters respectively.