This is the bonus cache for the second Brentwood is Beautiful Adventure Lab.
This is also hidden on j2d2's 20th Geocaching Anniversary, so you can celebrate that as well.
Complete the Adventure Lab to discover the numbers needed to figure out the final coordinates. Make sure to note the Adventure Lab answers for the final.
N51 0A.BCD W114 0E.FGH
Make sure to bring a writing implement.
You can discover more spots for Brentwood Community artwork here: Brentwood Is Beautiful Map