A simple pendulum of string length \( 30 \, \text{cm} \) performs \( 20 \) oscillations in \( 10 \, \text{s} \). The length of the string required for the pendulum to perform \( 40 \) oscillations in the same time duration is _______ \( \text{cm} \).
[Assume that the mass of the pendulum remains same]
