How to use airport panel information on sectional chart?
In addition to @JWalters's answer:
L-2F, 3B is one group, and it refers to the &quot;Enroute Low Chart Number(s) and Panel Identification&quot;,$^1$ that is:

L-2F, and
L-3B.

Since you are aware of the L-2F, here's the L-3B:

Source: skyvector.com

$^1$ Interagency Air Committee (IAC) Specifications, IAC 8, faa.gov, § 3.1.5.2.7