Density (D) is the obtained quotient when the mass (m) of the substance is divided by the volume (v) it occupies.
D = m / v ; m = D x v
Assuming that the given density has a unit of grams per mL and substituting the known values to the equations,
m = (3.1 g/mL) x 25 mL
m =77.5 grams
Thus, the answer is 77.5 grams.