There were 3 different fish caught, Salmon, Herring and Flounder.
4/9 were Herring, 2/9 were Salmon, 4/9 +2/9 = 6/9
This means 3/9 were Flounders ( 3/9 + 6/9 = 9/9 = 1)
3/9 can be reduced to 1/3.
1/3 of the fish were Flounders.
Divide the amount of flounders by the portion caught:
12 / 1/3 = 12 * 3/1 = 36 total fish.
Now you have total number of fish, multiply the total by each portion for each type of fish.
Total fish = 36
Herring = 4/9 x 36 = 16
Salmon = 2/9 x 36 = 8