Final answer:
By adding the number of fish fed to the dolphins at two different times, we find that the dolphins were fed a total of 906 fish, with the closest estimate being 900 fish.
Step-by-step explanation:
To estimate the total number of fish the dolphins ate, we simply need to add the two amounts given: 103 fish at 9:00 a.m. and 803 fish at 5:00 p.m. When we add these two numbers together, we get a total of 906 fish (that is, 103 + 803).
Given the multiple-choice options, the closest estimate to 906 is 900 fish, which means the correct answer would be option B).