The period formula, Eq. $$T=2\pi \sqrt{I/mgh}$$, requires knowing the distance $$h$$ from the axis of rotation and the center of mass of the system. We also need the rotational inertia $$I$$ about the axis of rotation. From the figure, we see $$h = L + R$$ where $$R = 0.15m$$. Using the
parallel-axis theorem, we find
$$I=\dfrac{1}{2}MR^{2}+M\left ( L+R \right )^{2}$$.
where $$M =1.0 kg$$. Thus, $$T = 2.0s$$, leads to,
$$2.0=2\pi\sqrt{\dfrac{\dfrac{1}{2}MR^{2}+M\left ( L+R \right )^{2}}{Mg\left ( L+R \right )}}$$.
which leads to $$L = 0.8315 m$$.