How to access another network through gateway PC?

Question

Windows

An exemplary scheme is shown in the figure. There are two networks in the enterprise, connected by machine B with two network interfaces. Normal routing is configured between machines A and B , but not between machines B and C ; everything works on broadcasting (the network was built a long time ago, and it cannot be changed).
You need to get access from machine A to machine C , preferably using static routes. Tell me what and where to do / register?
Adding a route on machine A of the form route ADD 192.168.3.111 MASK 255.255.255.255 10.240.72.32and many other variations had no effect. I understand routing poorly, but there was such task. Thanks for any advice.

Answer 1

It is necessary to insist routes in two places: 1) to A to network C through B and 2) to C to network A through B

Answer 2

Need to get access from machine A to machine C,

Well, first you need to make computer B (the one with two cards) a router. Is it your router? What is the OS on it?
And after that, you need to register routes on machines A and C, specifying computer B as the gateway.