The percentage error, also known as percent error, is a measure of how inaccurate a measurement is, standardized to how large the measurement is. It is the relative error expressed in terms of per 100.
The solution would be like this for this specific problem:
% error= |(55.0g − 56.0g) / 55.0| × 100 = 1.82%
I hope this helps and if you have any further questions, please don’t hesitate to ask again.