Can somebody please help me how to solve this question?

A marshy region used for agricultural drainage has become contaminated with a particular element. It has been determined that flushing the area with clean water will reduce the element for a while, but it will then begin to build up again. A biologist has found that the percent of the element in the soil x months after the flushing begins is given by the function below. When will the element be reduced to a minimum? What is the minimum percent? f(x) = x2 +49 4x -, 1Sx$ 12 Find f' (x). f'(x) = When will the element be reduced to a minimum? The element will be reduced to a minimum after month(s). What is the minimum percent of the element? The minimum percent of the element will be%. (Type an integer or a decimal.)