Let x denote the length of the side of the garden which is bounded by a river, then other (adjacent) side of the farmland has a measure of

.
The perimeter of a rectangle is given by 2(length + width).
Given that one of the sides is to be bounded by a river, the the perimeter of the remaining three sides to be fenced is given by

Given that there is 1,900 m of wire available to bound the three sides, then the perimeter of the three sides is equal to 1,900
Thus

For the area to be maximum, the differentiation of A with respect to x must be equal to 0.
i.e.

Therefore, the maximum area of the garden enclosed is given by

The dimensions of the farmland is 950m by 451,250 / 950 = 950m by 475m