You'll need to give a bit more information for the question to be answered. You can only calculate the percentage of error if you know what the mass of the substance *should be* and what you've *measured* it to be.
In other words, if a substance has a mass of 0.55 grams and you measure it to be 0.80 grams, then the percent of error would be:
percent of error = { | measured value - actual value | / actual value } x 100%
So, in this case:
percent of error = { | 0.80 - 0.55 | / 0.55 } x 100% percent of error = { | 0.25 | / 0.55 } x 100% percent of error = 0.4545 x 100% percent of error = 45.45%
So, in order to calculate the percent of error, you'll need to know what these two measurements are. Once you know these, plug them into the formula above and you should be all set!
