How to arrive at answer of 138.2???

You are an environmental engineer working for a consulting firm. Your firm was hired by the water treatment plant to recommend emergency measures when the intake water received an unusual spike of a pollutant. You want to recommend a process that can degrade the chemical with a first order kinetics rate constant k of 1(hour1). The plant used a completely mixed flow reactor with volume V=1000m3 and Q=10000hrm3. Instead of using the existing CMFR, you are thinking about using one ideal plug flow reactor. Calculate the hydraulic resident time in minutes of this PFR so that only p=10% of the chemical was left in the effluent. (a) 25.8 (b) 0.5 (c) 19.5 (d) 45.8 (e) 138.2