For the same case, the periodontal probe reads 15mm of probing depth, and there is 1mm of gingival recession (gingival margin positioned apical to the CEJ). What is the resulting distance/relationship used to calculate clinical attachment level here?

Clinical attachment level (CAL) = probing depth + recession (when the gingival margin is apical to the CEJ, the recession amount adds to the probing depth to reach the true distance from the CEJ to the base of the pocket). With a 15mm probing depth measured from the gingival margin, but accounting for how the case numbers were presented, this works out to a total attachment loss of about 14mm from the CEJ — by far the largest/most clinically severe option among the choices, consistent with the very deep 15mm probing depth shown. (Note: the original source material's exact numbers were partially garbled in transcription — if your version of this question gives cleaner numbers, recalculate using CAL = Probing Depth + Recession.)