Figure 4: The values of net present value (NPV), payback period (PBP), and rate of return (ROR) with the selling prices of products: (a) NPV ≥ 0 for manufacturing PC with an approximate selling price ≥ $0.72/lb PC; (b) NPV ≥ 0 for manufacturing PPC with an approximate selling price ≥ $0.97/lb PPC.