1099B Cost Basis Analysis

Hello. I received a 1099B from DWS, after withdrawing $6K last year. This is a long-term stock fund that I invested in over several years starting in 1990.

 

On my 1099B form from DWS there is no cost basis entered in Box 1E, and no Dated Acquired in Box 1B. I'm trying to figure out my Cost Basis and enter it in Turbo Tax Box 1E. My question is in the calculation of cost basis.

 

i.e. If I acquired 150 shares of Stock X in 1990 @ $20 a share.

Sold same 150 shares of Stock X in 2024 for a lesser amount of $15 a share, would my cost basis go like this?

 

1990=$3000

2024=$2250

Cost Basis=$750

Is this how you do it? Also, if shares were purchased on different dates at different stock share amounts, can you take the average?

 

Thank you.