Answer
$1.4 * 10^{6} \frac{g}{cm^{3}}$
Work Step by Step
Since the problem specified that the density needs to be put into grams per cubic centimeters, let's convert the radius into cm. Each km is 100000 cm, So we take the $7.0 * 10^{5}$ km and multiply it by 100000. We end up with $7.0 * 10^{10}$ cm. Also, since the units must be in grams per cubic centimeters, let's convert the mass of the star into grams. 1 kg is 1000 g, so $2.0 * 10^{36}$ kg would be multiplied by 1000 to result in $2.0 * 10^{39}$ g. We know that the density is calculated by dividing the mass by the volume. Recall that the volume of a sphere is calculated through this equation: V = $\frac{4}{3}$$\pi$$r^{3}$. Plugging in the radius in cm that we calculated above, we calculate that the volume of the star is $1.4 * 10^{33} cm^{3}$. Finally, take the mass in grams that we calculated above and divide it by the volume we just calculated. This results in this answer for the density: $1.4 * 10^{6} \frac{g}{cm^{3}}$
