Moment of inertia

Find the moment inertia of a thin rectangle with sides $$a, b$$ and mass $$m$$ around axis perpendicular to the picture and pass through the centar of rectangle.

Hint: Moment of inertia of the rod around axis passing through his centar is $$I=\frac{ml^2}{12}$$ where $$l$$ is the lenght of the rod.

$$a=3, b=4, m=12$$

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