Will the focal length of a lens for red light be more,same,or less than that for blue light?

(A) According to the lens maker's formula,the focal length $f$ is given by:
$\frac{1}{f} = (\mu - 1) \left[ \frac{1}{R_1} - \frac{1}{R_2} \right]$
Since the term $\left[ \frac{1}{R_1} - \frac{1}{R_2} \right]$ is constant for a given lens,we have $\frac{1}{f} \propto (\mu - 1)$,which implies $f \propto \frac{1}{\mu - 1}$.
According to Cauchy's dispersion formula,the refractive index $\mu$ is higher for light of shorter wavelengths (blue) and lower for light of longer wavelengths (red).
Thus,$\mu_b > \mu_r$.
Since $f$ is inversely proportional to $(\mu - 1)$,a higher refractive index results in a smaller focal length.
Therefore,$f_r > f_b$. The focal length for red light is more than that for blue light.