= Solution
<copper>(I) converts the methyl <grignard reagent> into a softer organocopper <nucleophile>. Methyl undergoes \b[1,4 addition] to the beta <carbon> of the cycloheptenone, giving a metal <enolate> rather than direct 1,2 addition to the <ketone> <carbonyl>.
The <carbon> nucleophilic site of this <enolate>, at the alpha <carbon>, attacks the <aldehyde> <carbonyl> in the second reagent. Its C=O $\pi$ <electrons> move to <oxygen>; <protonation> of the resulting <alkoxide> gives the beta-hydroxy <ketone> side chain. The cyclic <acetal> is a protected <ketone> and survives these nucleophilic conditions.
The beta <methyl group> shields one face of the cyclic <enolate>. Aldol bond formation from the less crowded opposite face places the new alpha side chain \b[trans to the beta <methyl group>]. Thus the two starred ring centers have an anti relationship; the two mirror-related products are possible from achiral starting materials and reagents. This argument does not assign the separate, unstarred <alcohol> center, for which the question gives no specified configuration.
\Image[/past-exam-of-the-chemistry-b-course-of-the-university-of-cambridge/2021/paper-1-b2-stereo.png]
{title=Conjugate methyl addition followed by opposite-face aldol trapping of the cyclic enolate}
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