Algebra word problem! Help?

annik

A farmer plans to use 180 feet of fencing to enclose a rectangular region, using part of a straight river bank instead of fencing as one side of the rectangle. Find the area of the region if the length of the side parallel to the river bank is

a) twice the length of an adjacent side.

b) one-half the length of an adjacent side.

c) the same as the length of an adjacent side.

There is an illustration, which is basically three sides of fencing and where the fourth side should be, it's just a river bank.

Update:

Please also show me the steps if you can! Thank you!

anonymous

a) 4050 ft sq.

b) 2592 ft sq.

c) 3600 ft sq.