Split horizon will prevent 192.168.10.0/24 from being advertised into the RIP domain from the IGRP domain.
2
No, because not all subnets of 10.0.0.0 are directly connected to Mantle on the RIP side.
3
The network statement under Robinson's EIGRP 1 configuration matches interface 192.168.3.32, even though no EIGRP Hellos are being forwarded out that interface. Therefore, the subnet is advertised as internal within the EIGRP 1 domain.
4
EIGRP automatically entered this summary route because subnets of 192.168.3.0 are being redistributed into EIGRP from OSPF.
5
A level-1 router in area 1 will not know of the summary route. RIP is being redistributed into level-2 (this is the default distribution level). The summary-prefix command is summarizing routes that are getting advertised into level-1.