"marginal benefit" is most related to what economic concept?

Dozier company produced and sold 1,000 units during its first month of operations. it reported the following costs and expenses for the month: direct materials $ 69,000 direct labor $ 35,000 variable manufacturing overhead $ 15,000 fixed manufacturing overhead 28,000 total manufacturing overhead $ 43,000 variable selling expense $ 12,000 fixed selling expense 18,000 total selling expense $ 30,000 variable administrative expense $ 4,000 fixed administrative expense 25,000 total administrative expense $ 29,000 required: 1. with respect to cost classifications for preparing financial statements: a. what is the total product cost