Quick way to find and highlight several hundred rows of data/and add data to new column

Hi

I tried asking this on Friday and didn't get an answer. I'll try asking again.

I have a spreadsheet with a column of contract numbers. Some of these contract numbers need to be highlighted in yellow, and a second column inserted with contract numbers they are linked to. The list of contract numbers and contract numbers they are linked to is in a separate spreadsheet with only two columns: Contract Number; Linked Contract Number. I've provided a sample spreadsheet with what I have NOW and then what I WANT the spreadsheet to look like. Basically, the second version needs to have the "Linked Contract Number" inserted into a currently-blank column I've created called "Linked Contract Number," and then have all of the rows with a value in "Linked Contract Number" highlighted. I hope this makes sense; apparently it didn't make sense to people on Friday.

There are too many values to use "find" and manually type the linked contract # in a new column in a reasonable amount of time.

Sample spreadsheet attached

Thanks for your help!