Please help me i cannot get this right $.$ Perpetual inventory using FIFO

Beginning inventory, purchases, and sales data for prepaid cell phones for December are as follows:

Inventory

Dec. $1320$ units at $$31$

Purchases

Dec. $10160$ units at $$33$

$20144$ units at $$35$

Sales

Dec. $12224$ units

$14192$ units

$3196$ units

units are in inventory at two different costs, enter the units with the LOWER unit cost first in the Cost of Goods Sold Unit Cost column and in the Inventory Unit Cost column.

FIFO Method

Prepaid Cell Phones