How to add default gateway to a interface

Linux Basics Course
#1

In Lab: Network basics

Question 11:
While we are at it, there is also a missing default route on the server devapp01.
Add the default route via eth0 gateway.

Answer:
To add the default route via eth0 gateway, run the following command:

sudo ip r add default via 172.16.238.1

Why the ip is 172.16.238.1? how to get this IP from eth0? Can anyone explain this for me? thank you

#2

In question 3 you already determined what the network’s default gateway is.