We recall the fitted model to our differential equation solution, Pcost(t).

Plot[Pcost[t],{t,0,200}]

Input := 


solPcost = FindRoot[Pcost'[t]==0,{t,40}]

Output =


{t -> 27.5171}

Input := 


Pcost[t]/.solPcost[[1]]

Output =


1.84894