= Solution
The <arene> and three <carbonyl ligands> are neutral, so \b[<chromium> is in <oxidation state> zero], with a $d^6$ <metal> count. The eta-six <arene> contributes six <electrons> and each CO contributes two:
$$
\boxed{6+6+3(2)=18\text{ valence electrons}.}
$$
The <methoxy group> changes the electronic properties of the <arene> without changing this formal <electron> count. The complex is a <piano-stool complex>, with the coordinated <arene> as the seat and the three <carbonyl ligands> as the legs.
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