= Solution
At 400 MHz, a separation $\Delta\delta$ in ppm corresponds to $J=400\Delta\delta$ Hz. The two multiplets near 5.10 and 4.47 ppm each have a quoted separation of 0.02 ppm, giving \b[$J\simeq8$ Hz]. The multiplets near 4.625 and 3.865 ppm each have separation 0.01 ppm, giving \b[$J\simeq4$ Hz]. These are approximate values from the rounded peak labels.
The fused unsaturated/aromatic framework restricts the five-membered ring, as in the comparison in (a). Assign the larger coupling to \b[cis] and the smaller to \b[trans]. Matching equal couplings and integrals pairs the 5.10/4.47 signals with one another, and the 4.625/3.865 signals with one another. The integral ratio is
$$
\boxed{\mathrm{cis:trans}=0.7:1.0\simeq41:59}.
$$
With an achiral substrate and achiral catalytic environment, each <diastereomer> is expected as a racemic enantiomeric pair: cis $(2R,3S)/(2S,3R)$ and trans $(2R,3R)/(2S,3S)$. The reported spectrum requires both <diastereomers>; the reagent label alone cannot override that evidence. Their ratio does not establish whether the selectivity arose in the initial surface addition or after product <epimerization>.
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