$\dfrac{L_c}{I} = \dfrac{20}{D}$
$\dfrac{L_{c1}}{24^\circ} = \dfrac{20}{6^\circ}$
$L_{c1} = 80 ~ \text{m}$
$\begin{align}
\text{Sta.} ~ P.C.C & = \text{Sta.} ~ P.C. + \, L_{c1} \\
& = (10 + 420) + 80 \\
& = \text{km} ~ 10 + 500
\end{align}$
Answer: [ D ]
