Hello subarudad and welcome to the forum.

There are two different sets numbers stamped around each side of the bottom bracket shell.

It appears that the left side is R902400730. This serial number is from The Derby Cycle Corporation, who purchased West Coast Cycle in about 1989. The serial number has an encoded date beginning with the the first digit.

9 - decade
024 - day of the year.
0 - year of the decade.

Day 24 of 1990, for the date of the bicycle assembly.

The number on the right side is probably the serial number of the frame manufacturer. I cannot see enough of this number to determine the manufacturer.

The Derby Cycle Corporation distributed bicycles with several brand names. Derby Cycle purchased frames from various manufacturers.

I do not know this as a fact, but I suspect that the frames were sent to the factory in Kent, Washington for assembly and this is where the "R" prefix number was stamped onto the BB shell.

Do you have a picture of the headbadge?