Answer: 27.791 meters
Explanation: The precision of a measure depends on the number of significative decimals that it has, so the number that is most exact is the one with more numbers after the decimal point, in this case, is the third option: 27.791 m
This one is the most exact because you know that the lenght is:
27 meters, 7 centimetrs and 9.1 milimeters