Alium - marks racers with high odds (x100, x50, probably no lower) if they'll be within top 2.

Calla - accurately marks racers that have not been marked with a double circle or a special mark by other predictors.

Starting off, Alium's prediction seems accurate.
Each of the predictors marked one of the three highest racers odds-wise, but only one of them will be in top 2 - this means that almost certainly x50 will win the next race.
Just to be safe, I've also bet on Calla's prediction, in case x30 is not considered as "high odds" for Alium. In this case there's a small chance that x50 will take 2nd place and x30 will win.
Nazuna's prediction goes to x100 (the highest odds), but it was not marked by Alium, therefore this racer will not win.