$ sudo apt-get update
$ sudo apt-get install libpanel-applet-4-dev 

libpanel-applet-4-dev is installed in your system.

Make ensure the libpanel-applet-4-dev package were installed using the commands given below,

$ sudo dpkg-query -l | grep libpanel-applet-4-dev *

You will get with libpanel-applet-4-dev package name, version, architecture and description in a table

libpanel-applet-4-dev package basic information: