Which is the most efficient summarization that R1 can use to advertise its networks to R2?

Network 172.1.4.0/25 and network 172.1.4.128/25 can be grouped to a single network 172.1.4.0/24 By looking the other networks you will notice that our increment is 4 since the network address are 4 , 5 , 6 , 7 , so to achieve the increment 4 we need to modify our subnet mask to be 255.255.11111100.00000000 and that is /22

So the Summary would be 172.1.4.0 /22