Could anybody provide some guidance or steps for this physics problem? It would be much appreciated?

A uniform rectangular sign of width 48.6 cm, height 25.6 cm, and negligible thickness hangs vertically from supporting hinges attached at its upper edge. Find the period of small-amplitude oscillations of the sign. I know that this is a pendulum, and that the formula T = 2pi (L/g)^(1/2) can probably be used. I... show more A uniform rectangular sign of width 48.6 cm, height 25.6 cm, and negligible thickness hangs vertically from supporting hinges attached at its upper edge. Find the period of small-amplitude oscillations of the sign.

I know that this is a pendulum, and that the formula T = 2pi (L/g)^(1/2) can probably be used. I tried the following:

Exponential 1/2 = square root of L/g
L = 0.5 times (0.256) <-- cm to m
g = 9.8
Neither the width nor the mass matter as they do no appear in the formula

The answer is supposed to be 0.829 sec

Any advice on where I went wrong?
Update: There are two other formulas which may be the correct ones to use: α=−((mgd)/I)*θ and T=2π(I/(mgd))^(1/2)

If either of these are the correct formula, I am not sure how to use them, particularly with I and θ
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