.55 is the answer. I hope this helped a great deal!
868 is about 870, and 28 is about 30, so your expression would be 870 divided by 30 which would be 29 and the actual answer is 31, so your estimate would be close to your actual answer.
What are you trying to prove here? I know when step will be the use of the Transitive Property. If a=b, and b=c, then a=c.
