I'm having difficulties understanding the solution to the following question:

Consider the following description of a LAN:

The main Internet connection is connected to our gateway router. This in turn is part of the backbone network on the 65.21.1.0/24 subnet. The backbone also supports two further routers SALES and RESEARCH. There is one Sales subnetwork 65.21.6.0/23, and two research subnetworks 65.21.100.0/24 and 65.21.200.0/26.

If the Interface addresses are:   

• i1–65.21.1.1
• i2–65.21.1.2
• i3–65.21.6.1
• i4–65.21.1.3
• i5–65.21.100.1
• i6–65.21.200.1

What are the routing tables for the SALES and RESEARCH routers?

How is the via and interface column derived in the solution?

Thanks in advance.