Answer
$2.70g/cm^3$
Work Step by Step
We have the side of a cube in $mm$ and we need volume in $cm^3$
$15.6mm*\dfrac{cm}{10mm} = 1.56cm$
volume $= (1.56cm)^3$
volume $= 3.7964cm^3$
density $= \dfrac{10.25g}{3.7964cm^3}$
$$2.70g/cm^3$$