.
The inequalities are
L >= 10 ft (length)
W >= 5 ft (width)
2L + 2W = 50 ft (perimeter) or, equivalently
L + W = 25 ft.
The graph showing possible dimensions of her garden is presented in the Figure below.
The horizontal axis is L. Vertical axis is W.
Plot L + W = 25 (red), L = 10 (green) and W = 5 (blue)
The solution set is the straight line segment = the hypotenuse of the triangle, shown in red.
The two possible combinations are the highest vertex of the triangle and the rightmost vertex of the triangle.
Try to cipher these points on your own.