The gravitational force between the two objects is given by: [tex]F=G \frac{m_1 m_2}{d^2} [/tex] where [tex]G=8.99 \cdot 10^{-11} m^3 kg^{-1} s^{-2}[/tex] is the gravitational constant [tex]m_1 = 1.99 \cdot 10^{30} kg[/tex] is the Sun mass [tex]m_2 = 3.30 \cdot 10^{23} kg[/tex] is the mass of Mercury and d is the distance between Sun and Mercury. Since we know the force: [tex]F=8.99 \cdot 10^{21} N[/tex] we can re-arrange the formula to find d: [tex]d= \sqrt{ G \frac{m_1 m_2}{F} }=6.98 \cdot 10^{10}m [/tex]
