If a bag contains 12 apples,4 bananas, and 8oranges, what part-to-whole rational oranges to all fruit

So there are 8 total oranges, so your ratio is...
8:?

There is 16 other fruit (12 Apples, and 4 Banana) But we need to include the number of oranges (8) as it says "to all fruit" which should include oranges as well. So 16 + 8 = 24.
Your ratio is 8:24 or 1:3

The answer is $9.90 with rounding to the nearest tenth