Assigning R/S configurations to Fischer projections of 3‐chloro‐2‐hydroxybutanoic acid
The compound mentioned is (2S,3R)-3-chloro-2-hydroxybutanoic acid. For Carbon atom #2, the CIP priority order is

$\ce{Cl}$
Carbon #1
$\ce{CH3}$
$\ce{H}$

The methyl group is lower priority because Carbon #1 has a hydroxyl group attached to it, which is higher priority than Hydrogen. This implies that the orientation at carbon atom #2 is R.
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