How to add a device from another network to the local network?

Question

Computer networks

What settings need to be done with the wlan0 and eth0 interface so that 3 can be pinged from 1 computer?

Answer 1

On computer 1, specify the router as the default route or register the route to computer 3 through the router.
On computer 2, enable routing.
On computer 2, specify the router as the default route or register the route to computer 1 through the router.
On computer 3, specify computer 2 with the default route or register a route to computer 1 through computer 2.
On the router, register a route to computer 3 through computer2.

Answer 2

Configure packet forward with masquerading between eth0 and wlan0 for the desired addresses and routing on the router.