$${\frac{m_S}{m_P} = \frac{\text{pindala}_S}{\text{pindala}_P} = \frac{\text{pindala}_S}{\text{pindala}_C - \text{pindala}_S} \\= \frac{\pi R^2}{ \pi (2R)^2 - \pi R^2} = \frac{1}{3}}$$