Cost of parts sold from wreck cars

[mightmen16]

I have a client who buys junk cars and sells the parts off of them. He has his sales and expenses, but also the cost of all of the cars that he has bought. How do you determine the cost of the parts that he sold?
If I use the total of cars that he bought, it will wipe out all income and give him a big loss? Hope someone has some ideas?

[spanel]

Cost of Goods sold.

Total dollar amount Cars bought 2018
Total parts salvaged from cars 2018
Divide parts/by $$ cars
This will give you approx cost per part.
What is not sold go under COGS inventory.

Chris