Determine image distance relative to lens

[phys62]

Homework Statement

Two identical diverging lenses are separated by 13 cm. The focal length of each lens is -6.5 cm. An object is located 3.0 cm to the left of the lens that is on the left. Determine the final image distance relative to the lens on the right.

Homework Equations

1/i + 1/o = 1/f

1/i = 1/f - 1/o

The Attempt at a Solution

1/i = 1/-6.5 - 1/3
i= -.487

13 + .487 = 13.487 cm

I feel like I'm not doing this right at all.. can someone please let me know if I'm even on the right track?

 

[rl.bhat]

13 + .487 = 13.487 cm
This is the object distance for the second lens. Find the final image distance from the second lens.

 

[phys62]

Ok so I took 1/13.487 + 1/i = 1/-6.5

and I solved for i and got -4.386 cm.

Is this correct, or should I have used -13.487 and got -12.547 as my answer?

 

[rl.bhat]

and I solved for i and got -4.386 cm.
This is correct.

 

[phys62]

It's telling me that answer is incorrect.. I guess I'll try the -12.547 next

 

[rl.bhat]

1/i = 1/-6.5 - 1/3
i= -.487
Check this calculation.