An object is 21 cm in front of a diverging lens that has a focal length of -13 cm. How far in front of the lens should the object be placed so that the size of its image is reduced by a factor of 1.5?

my work:
1/di=(1/-13)-(1/21)
di=-8.02
m=8.02/21
m=.381
m2=-.381/1.5
m2=-.254
1/13=(1/do2)+(1/.254do2)
and this is where i get lost

I have tried to figure it out by finding the magnification, then trying to find m2, but in the process of doing this problem, I just get lost and confused, any help is greatly appreceated, thanks!