7.4*10^3g/dm^3
=7.4*10^3*10^(-3)kg/(10cm)³
=7.4*10^(-3)kg/cm³;
17g/mm^3
=17*10³mg/[10^(-3)m]³
=17*10³mg/[10^(-9)m³]
=17*10^(3+9)mg/m³
=17*10^12mg/m³
=1.7*10^13mg/m³
21mg/m^3
=21*10^(-3)g/(10dm)³
=21*10^(-3)*10^(-3)kg/(10dm)³
=21*10^(-6)kg/(10³dm³)
=21*10^(-6-3)kg/dm³
=21*10^(-9)kg/dm³
=2.1*10^(-10)kg/dm³