Answer:
option C
Step-by-step explanation:
given,
Beginning inventory       10 units @ $10 per unit
First purchase             35 units @ $11 per unit
Second purchase          40 units @ $12 per unit
Third purchase            15 units @ $13 per unit
first sale = 20 units
second sale = 35 units
now,
unit left after first sale = 35 - 20 = 15 units @ $11 per unit
unit left after second sale = 40 - 35 = 5 @ $12 per unit
third purchase = Â 15 units @ $13 per unit
inventory  = 10 units @ $10 per unit + 15 units @ $11 per unit + 5 @ $12 per unit + 15 units @ $13 per unit
        = 100 + 165 + 60 + 195
        = $ 520
hence, the correct answer is option C