Resolving power of a microscope is the shorter distance between two seperate point in a microscope's field of view that can be seen directly.
Resolving power \(\propto \frac{\lambda}{2 a}(a=\) aperture \()\)
\(\frac{d_1}{d_2}=\frac{\lambda_1}{\lambda_2} \Rightarrow \frac{0.05}{d_2}=\frac{6000}{3000} \Rightarrow 0.025\,mm\)