Let
x-------------> length of the fence
y-------------> width of the fence
we know that
Area of rectangle=x*y
perimeter of rectangle=2x+2y
A=250 ft²
P=68 ft
then
250=x*y-----------> x=250/y equation 1
68=2x+2y-----------> equation 2
using a graph tool---------> to resolve the system of equations
see the attached figure
the solution is the point 1 (10.755,23.245) and the point 2 (23.245,10.755)
for the point 1
x=10.755 ft
y=23.245 ft
for the point 2
x=23.245 ft
y=10.755 ft
the answer is
the dimensions of the fence are
23.245 ft x 10.755 ft
or
10.755 ft x 23.245 ft