The net weight is 215g. The weight of one envelope is 4.3 g or 4300 mg.
Work Step by Step
Subtract the weight of the packaging to find the net weight of the 50 envelopes. $255g-40g=215g$ Divide by the number of envelopes to find the weight per envelope. $215g\div50=4.3g$ Move the decimal to convert g to mg. $4.3g=4300 mg$