The given question asks to identify the proportions that are equal to 8/9. To determine this, we need to simplify each proportion and check if it equals 8/9. Simplifying 16/18 gives us 8/9, so it is equal to the desired proportion. Simplifying 56/81 results in a different value, so it is not equal to 8/9. Similarly, simplifying 24/27 gives us 8/9, so it is correct. Lastly, simplifying 80/90 gives us a different value, so it is not equal to 8/9. Therefore, the correct answers are 16/18, 24/27, and 80/90.