First let as solve all unit pirce whistles 21.25 / 25 = $ 0.85 per unit 36 / 50 = $ 0.72 per unit 60 / 80 = $ 0.75 per unit kazoos 10 / 25 = $ 0.4 per unit 18.50 / 50 = $ 0.37 per unit 27.20 / 80 = $ 0.34 per unit a.) $ 0.85 - $ 0.72 = $ 0.13 b.) 10 / 25 = $ 0.4 per unit c.) he must order 80 kazoos she should order