How to decide from the solubility product constants which hydroxide precipitates first?
If the question is about what compound would precipitate first, then there can be at most one answer.

Given equal stoichiometry  for the precipitation of $\ce{Fe(OH)3}$ and $\ce{Al(OH)3}$ and solubility product constants of $6 \cdot 10^{38}$ and $4 \cdot 10^{15}$ respectively, $\ce{Fe(OH)3}$ will be the correct answer.

$$\ce{Fe^{3+}_{(aq)} + 3 OH^{-}_{(aq)} -&gt; Fe(OH)3_{(s)}}$$

However, in practice the precipitate will probably contain less water than stoichiometric $\ce{Fe(OH)3}$, and also contain small amounts of $\ce{Al(OH)3}$