Answer: the density of ivory in SI units is 1800 kg/m^3.
Explanation: To calculate the density of ivory in SI units, we use the formula density = mass/volume. We are given the mass of 25 cm^3 of ivory as 0.045 kg. Since volume is in cm^3, we need to convert it to SI units of m^3. 1 cm^3 is equal to 1 milliliter (ml), so 25 cm^3 is equal to 25 ml. To convert ml to m^3, we use the conversion factor 1 ml = 10^-6 m^3. We then substitute the values of mass and volume into the density formula and simplify. The resulting density is expressed in units of kg/m^3, which are the SI units for density. Therefore, the density of ivory in SI units is 1800 kg/m^3.