Getting-Started with Brother MFC-7420 Fax on Ubuntu Linux
The Article Include Links to Download and Installation Guide for Brother MFC-7420 Printer/Fax Driver on Linux Ubuntu 14.04 Trusty Tahr LTS i386/amd64.
The Brother MFC-7420 Quick-Start Guide for Ubuntu Include also How-to Download and Install the MFC-7420 Printer Ubuntu Linux Driver.
Download Brother FAX .deb Drivers for Linux:
How-to Install Brother MFC-7420 FAX/Printer Driver for Ubuntu: