Gravitation Force between two bodies is
F= G Mm/d2
G = Gravitational Constant ( fixed every where)
M= Mass of spaceship =3.16* 108
Force = mass *acceleration =m*a , where a = Acceleration of wrench
m = mass of wrench
a = G*m/d2
d = √ ( G*M/a)
Now plug in values given
and G= 6.67259 x 10 -11 N m 2 /kg 2.
M = 3.16* 108 kg and a= 6.43*10 -7 m/s2
You get your answer in m ( Distance between two centers)