Chris Co$.$ produces surfboards. A customer has offered Chris Co$.$ $$400$ per unit for $100$ units. To fill the order, Chris would incur unit$-$level costs of $$350$ per unit and batch$-$level costs of $$5,500.$ Chris Co$.$ also incurred $$70,000$ of product$-$level costs to design the board and $$10,000$ of facility$-$level costs. Calculate the amount of differential revenue.