SOH CAH TOA tells you ...
... Tan(θ) = Opposite/Adjacent
You have ...
... Tan(θ) = (3)/(4)
Matching parts of the two expressions, we see ...
... Adjacent = (4)
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In the context of this problem we might reasonably assume that the adjacent side length is 4 units. In any other context, the best we might say is that it is 4/3 times the length of the opposite side.
