The meso epoxide shown is opened with sodium methoxide in methanol by clean backside $\mathrm{S}{}_{\mathrm{N}}2$ attack. Attack can occur at either epoxide carbon. Count the distinct stereoisomers of 3-methoxybutan-2-ol that are actually formed (enantiomers counted separately). Give your answer as an integer.

The compound is cis-2,3-epoxybutane (meso; RDKit confirms mirror-symmetric). The two epoxide carbons are enantiotopic (related by the internal mirror plane), so attack at one carbon gives one enantiomer of the product and attack at the other gives its mirror image. Both are formed in equal amounts, so 2 stereoisomers (a racemate) are obtained. For the trans epoxide the two carbons would be homotopic and only one product would form.