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I remember the problem so it's not a factor here, but remember that you need to include a copy of the problem you are solving.

The question asked for a differential approximation. You substituted 4.03 meters into the proportionality, and you got an accurate result, but did not use a differential approximation.

Class Notes #07 address the concept of the differential in a context very similar to the present. Please review that material and let me know if you have questions.

Then see if you can answer this question using a differential approximation.

This is important. It is on the test, and it's one of the central concepts in calculus.