To find the focal length of the eye lens in a compound microscope, we use the lens formula:

\(\frac{1}{f} = \frac{1}{v} - \frac{1}{u}\)

Given: Image distance from the eye lens: \( v_2 = 25.0 \, \text{cm}\)
Object distance for the eye lens (image from the objective lens): \( u = -3.0 \, \text{cm} \) (negative since it is on the same side as the incoming light)
\(\frac{1}{f} = \frac{1}{25.0} - \frac{1}{-3.0}\)
\(\frac{1}{f} = \frac{1}{25.0} + \frac{1}{3.0}\)
\(\frac{1}{25.0} = 0.04 \quad \text{and} \quad \frac{1}{3.0} \approx 0.3333\)
\(\frac{1}{f} = 0.04 + 0.3333 \approx 0.3733\)
\(f \approx \frac{1}{0.3733} \approx 2.68 \, \text{cm}\)

The focal length of the eye lens is approximately \( 2.68 \, \text{cm} \).