Linux Mint multi-display set-up 4k monitor

linux-monitor-config.txt

Monitor 1 (DP-2) 1920x1080, monitor 2 (DP-0) 3840x2160, monitor 3 (DVI-D-0) 1680x1050

Aligned along bottom horizontal of monitors with each monitor in landscape mode.

 - 1st go to Display settings and ensure all monitors are at max resolution, align monitors 
 roughly to the way you want your final configuration.

create: 
/opt/display.sh

#!/bin/bash

xrandr --output DP-2 --scale 2x2 --pos 0x0
xrandr --output DP-0 --scale 1x1 --pos 3840x0
xrandr --output DVI-D-0 --scale 2x2 --pos 7680x60

Set permissions:
chmod 755 /opt/display.sh

Set script to execute on start-up.