Set a static IP on Ubuntu Server 18+

/etc/netplan/01-netcfg.yaml
Add this

network:
    version: 2
    renderer: networkd
    ethernets:
        enp0s3:
            dhcp4: no
            addresses: [10.0.0.40/24]
            gateway4: 10.0.0.1
            nameservers:
                addresses: [8.8.8.8,8.8.4.4]

Bash this

sudo netplan apply
reboot