Can Anyone explain why and how do you get the answer. I saw another chegg post but i am confused on how it works.

Questions M7-6 and M7-7 are based on the following data: City Stationers Inc. had 200 calculators on hand on January 1, 2019, costing $18 each. Purchases and sales of calculators during the month of January were as follows: City uses a periodic inventory system. According to a physical count, 150 calculators were on hand at January 31, 2019. L0 7.5 The cost of the inventory on January 31,2019 , under the FIFO method is: a. $400 b. $2,700 c. $3,100 d. $3,200 LO 7.5 The cost of the inventory on January 31,2019 , under the LIFO method is: a. $400 b. $2,700 c. $3,100 d. $3,200