The Clearance of a Substance &;X&; is equal to the concentration of substance X in urine (UX) times the urine flow per unit of time (V) divided by the aerial plasma level of X (PX), or UXV/PX.This value is called the clearance of X (CX).Coming to the above question: 100 mg/dl X 2 ml/min / 10 mg/dl = 20 ml/min.