Find the angle in radian through which a pendulum swings if its length is 75cm and the tip describes an arc of length 15cm

Question

$\begin{array}{1 1}(A)\;\large\frac{1}{2}\normalsize radian&(B)\;\large\frac{1}{3}\normalsize radian\\(C)\;\large\frac{1}{4}\normalsize radian&(D)\;\large\frac{1}{5}\normalsize radian\end{array}$