A rectangular field is to be bounded by a fence on three sides and by a straight stream on the fourth side.
The fence as a whole must be equal to 1000ft and we assume that since it is a rectangle the two ends not facing the stream are equal. these ends will be given the variable x. Therefore, the equation for the dimensions of the field would be 1000-2x (the long side facing the stream), x (one end), and x (the other end). The area can be obtained by multiplying (1000-2x * x). Guess and check usually works to find the ideal x.