GNU/Linux Mint 19 Installing Broadcom BCM4331 Driver Guide
The linked tutorial shows you step-by-step How to Install Broadcom BCM4331 Wi-fi/Bluetooth Driver in Mint 19.x Tara/Tessa/Tina/Tricia LTS GNU/Linux.
The Package Provides the Source Code for the wl Kernel Modules and makes use of the DKMS Build Utility to Install them for the Running Kernel.

GNU/Linux Mint 19 Broadcom BCM4331 Driver Installation Guide