Assuming a rectangular area, let x = one side and y = the other.
Perimeter = 2(x+y) = 231
x + y = 115.5
y = 115.5 - x
Area = xy = 3000
x(115.5-x) = 3000
-x2 + 115.5x - 3000 = 0
Use the quadratic formula to get the values of x. The corresponding values of y are 115.5 - x.