1. the largest area of the rectnagle using 40m of fencing is 99m (9x11)
i found this answer by starting with a rectangle that was 15m by 5m, i then increased the length of the longest side and shortened the other side a few times to get my answer.
2. answer = 10 by 20
i started with 10 by 20 and then increased or decreased the numbers a few times to see if any were larger but there wasn't.
3. answer = 192m
i split the shape in half so that i could find the area,i then started with the numbers 12,26,2 i then continued trial and error to get the answer 18, 14 and 8 i then added the area of the other part of the rectangle and got the answer 192m.
extension:
if you had 40m of flexible wire fencing that could fence off curves as well as straight lines then you could enclose greater areas because then if there were round edges or curves then you be able to bend the fence in order to fence of the shape, however if the shape did not have any curves then it would be the same.