Since none of the chicken were not sold, you need to make the units the same therefore I times each other to make the units of chicken the same (note that while you are doing this you have to time the units in fish also) then now that the units of chicken are equal, you should be able to get 19u=57 as (28-9=19) after that you can find 1 unit by dividing 19. Finally, to find the mass of the fish at first, we need to times the units of fish(note that we should times the justified ratio at the bottom and not the initial ratio on the top)