What Focal Length Eyepiece Provides a -125 Magnification?

[Anna M]

Homework Statement

The medium-power objective lens in a laboratory microscope has a focal length fobjective = 3.75 mm.

What is the focal length of an eyepiece lens that will provide an overall magnification of -125? Assume student's near-point distance is N=25cm.

Homework Equations

M=(-di/fobjective)(N/feyepiece)

The Attempt at a Solution

I have set up my equation and plugged in all the known values, but I do not understand how to solve when you have 2 unknown values (di and feyepiece).

Part A of this question says: If this lens produces a lateral magnification of -46.0, what is its "working distance"; that is, what is the distance from the object to the objective lens?
I have worked Part A out, but I am not sure if they correlate and I am supposed to use values from that portion or if they are completely separate.

 

[Drakkith]

Yes, you need to use the working distance found in part A to solve part B. Otherwise you don't know $di$.
Generally, if a problem consists of more than 1 part, and you're missing a value for a later part, the missing value can be found using given information or your answers in previous parts. That's been my experience at least.