Ubuntu wifi driver problem - Broadcam Driver

1. update the system 

sudo apt update

sudo apt upgrade

2. Remove all the wifi source

sudo apt-get purge bcmwl-kernel-source

sudo apt-get remove bcmwl-kernel-source

3. Again install it

sudo apt install firmware-b43-installer
sudo apt install linux-firmware
sudo reboot

If not work then just reinstall this

sudo apt-get install --reinstall bcmwl-kernel-source