What the answer to this problem sue subtracted 2.9 from 20.9 and got 1.8.Explain why this is not reasonable?

Sue's calculation is not reasonable because when you subtract 2.9 from 20.9, the correct result is 18.0, not 1.8. The subtraction can be verified as follows: 20.9 - 2.9 equals 18.0. Therefore, her result of 1.8 indicates a significant error in her calculation.