Smith Company sells its products at $$500$ per unit, net $30.$ The firm's gross margin ratio is $40$ percent. The firm has estimated the following operating costs:

Smith Company has gathered the following data pertaining to activities it performed for two of its customers:

What is Smith's total sales$-$sustaining cost applicable to XBT as a customer?

Multiple Choice

$$4,120.$

$$920.$

$$6,300.$

$$6,420.$

$$0.$