Given the value of possible error, the relative error of the measurement is 0.0095.
Given the data in the question;
Relative error is simply the ratio of the absolute or possible error of a measurement to the measurement its self.
Relative error is expressed as;
[tex]RE = \frac{e}{m}[/tex]
Where e is the absolute or possible error and m is the measurement being taken.
To determine the relative error, we substitute our given values into the expression above.
[tex]RE = \frac{0.04cm}{4.2cm} \\\\RE = 0.0095[/tex]%
Therefore, given the possible error, the relative error of the measurement is 0.0095.
Learn more about relative error: https://brainly.com/question/17016021