Three part 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? x + 100 f(x ) = 1SXs 12 2x Find f'(x) f' ( x)=