Find the angle in radian through which a pendulum swings if its length is 75cm and the tip describes an arc of length 21cm

Question

$\begin{array}{1 1}(A)\;\large\frac{8}{25}\normalsize radian&(B)\;\large\frac{6}{25}\normalsize radian\\(C)\;\large\frac{7}{25}\normalsize radian&(D)\;\large\frac{9}{25}\normalsize radian\end{array}$