(N/A) The formula for gravitational force is $F = G \frac{m_1 m_2}{r^2}$.
Rearranging for $G$,we get $G = \frac{F r^2}{m_1 m_2}$.
$1$. $MKS$ unit: The unit of force is $Newton$ $(N)$,distance is $meter$ $(m)$,and mass is $kilogram$ $(kg)$. Thus,the unit is $N \cdot m^2 / kg^2$ or $kg^{-1} \cdot m^3 \cdot s^{-2}$.
$2$. $CGS$ unit: The unit of force is $dyne$ $(dyn)$,distance is $centimeter$ $(cm)$,and mass is $gram$ $(g)$. Thus,the unit is $dyn \cdot cm^2 / g^2$ or $g^{-1} \cdot cm^3 \cdot s^{-2}$.
$3$. Dimensional formula: Substituting the dimensions of force $[MLT^{-2}]$,distance $[L]$,and mass $[M]$ into the formula $G = \frac{F r^2}{m_1 m_2}$,we get $[M^{-1} L^3 T^{-2}]$.