#### Answer

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.
$4.3g=4300 mg$