You have to find the unit rate, which in this case means the amount of fish you need per serving of soup.
If 16 oz of fish makes 24 servings, then 16/24 oz = 2/3 oz makes 1 serving.
Now multiply both quantities by 10, so that 10 servings require 20/3 oz ≈ 6.67 oz of fish.
A more direct way to do this is to solve for x in the following equation:
(16 oz fish) / (24 servings) = (x oz fish) / (10 servings)
Then (omitting units)
x = 10 • 16 / 24 = 20/3
