By definitions of the prefixes in the metric system, the prefix milli- (abbreviated as m as in mg) indicates 1/1000 or 1 x 10^-3 of a gram. In this case, if a beaker has a mass of 77.275 g (I am assuming this is grams since most other units would make it too heavy or too light), we would multiply this by 1000 to convert it to milligrams. So 77.275 g = 77,275 mg.
