Board Thread:Game Discussion/@comment-2405:204:D08A:E544:29F8:E6C:1AAA:4278-20181021110612/@comment-32545704-20181021223844

https://rr3.wikia.com/wiki/Group_C_1988_Season

It's not easy to work out but you can do it using the ink above. There are 45 events which means you need to complete 34 to get 75%. In theory you could skip the 11 highest PR cups, but in practice this is unlikely as it depends on how the tiers unlock. You can check in game to see how many trophies are required to unlock each tier and work it out from there. Much easier though is to just do the races and find out.