For this one, we need to apply the Scale Property:

`Lap{f(at)}=1/aF(s/a)`

Here, `a = 3` so

`Lap{cos^2 3t}=1/3((s/3)^2+2)/((s/3)((s/3)^2+4))`

`=(s^2/9+2)/(s(s^2/9+4))`

`=(s^2+18)/(s(s^2+36))`

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