Thank you for the lesson is very interesting.
I did not understand the advertised distance of loopback on R2,R3,R4
If I understood correctly
FastEthernet=256*(100/10+10000000/100000)=28160
Loopback=256*(5000/10+10000000/8000000)=128320
The sum is 156480
Am I doing something wrong? Or have any values been customized?