The question simply asks for the proper equation to use for a non steady state system, please dont solve as thats not what its asking.

1. Consider a lake with the following characteristics: - Surface Area =11106m2 - Mean depth =5m - Residence Time =4.6yr - TSS=2mg/L (mass of suspended particulates per volume of water) - foc=0.4% An industrial plant presently discharges malathion (a pesticide) to the lake at a loading rate (W) of 2000106g/yr. In addition, the inflowing stream also contains malathion at 15mg/L. Your firm measures degradation of the pesticide in the lake water at a first-order rate of 0.1yr1. Log koc for malathion =2.61 Write the differential equation that represents the transient mass-balance equation for malathion for this system