Answer
$\dfrac{F(rm_1, rm_2)}{F(m_1, m_2)}=r^2$ and $\dfrac{F(rd)}{F(d)}=r^{-2}$
Work Step by Step
From the previous part (a), we have
$F= G\dfrac{m_1m_2}{d^2}$
As the masses of the objects increase the force increases and the $d$ is kept constant. When each of the masses gets increased by the common ratio, then $\dfrac{F(rm_1, rm_2)}{F(m_1, m_2)}=r^2$
As the distance between the objects increases, the force decreases. When the distance gets increased by $r$, then $\dfrac{F(rd)}{F(d)}=r^{-2}$
Hence, $\dfrac{F(rm_1, rm_2)}{F(m_1, m_2)}=r^2$ and $\dfrac{F(rd)}{F(d)}=r^{-2}$
