The Verhulst's logistic model has been applied to the natural growth of the halibut population in certain areas of the Pacific Ocean. Let NN, measured in kg, be the total mass (or biomass) of the halibut population at time tt. The parameters in the logistic equation are estimated to have the values r=0.71:per:year and K=80.5times10^6:kg. If the initial biomass is N_0=0.25K,N0=0.25K, Find the biomass 2 years later; also, Find the time tauτ for which Nleft(tauright)=0.75K.