Please do it fast

Justin's company produces earbuds. The marginal cost of making the 100th earbud is $75 and the average total cost of the 100th earbud is $80. What do we know about the average total cost curve at a quantity of 100? if\"; It is falling (decreasing). \\___/ ("a It is constant (horizontali. \\___/ (i) It is rising [increasing]. if"; It becomes a sunk cost. \\___/ /'_'\\ '1\\___,1' It is impossible to determine from the information given