Answer
$7.41*\mu N$
Work Step by Step
First we will make sure the units in equation 1-2 are dimensionally homogeneous.
$F=G \frac{m_1*m_2}{r}$
$F=(\frac{m^3}{kg*s^2}) \frac{kg*kg}{m}$
$F=kg *m^2 / s^2$
This checks out. These units are correct.
Given that the mass of each sphere is 200 kg and the radius is 300 mm, we will find the gravitational force between them
$F=G \frac{m_1*m_2}{r}$
$F=66.73*10^{-12} m^3 / kg / s^2*\frac{200kg *200kg}{0.600m}$
$F=7.41*10^{-6}N=7.41*\mu N$
