Column 1 has item numbers (About 3,000 of them) | column 2 has weights | MY COLUMN - column 3 has only item numbers I want.(About 1500 of them)

How do I find the item numbers that I have in column 3 in column 1 and delete the ones I dont want from column 1?

While keeping column 2 (the weights) matching the products in column 1

After I do that, I need to convert the weights from pounds to grams!

Can anyone help? ughhh I have no idea how to do this! Thank you for any help in advance!