A synthetic organic chemical, A, is found in a river section having a length of 3000 m, a velocity of 0.05 m/s, and a dispersion coefficient of 9.4 m2/s. This chemical is susceptible to rapid photochemical degradation. The reaction rate at a given light intensity is thought to be first order with respect to the concentration of A, but the rate constant has never been measured. If the concentration is reduced by 98% in this stretch of river how much decomposition can be expected in a more turbulent reach (with similar photochemical