# Simple pendulum and planet mass [closed]

A simple pendulum, $20cm$ in length, has the period of $2.7s$ on a certain planet. Find the mass of the planet if its diameter is $18000km$. $G=6.67\times10^{-11}Nm^2/kg^2$

I have no idea how to get to the solution except for the formula $$g=(GM)/(R^2)$$

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The next thing you'll need is time period of a simple pendulum $$T=2\pi\sqrt{\dfrac{L}{g}}$$