Indicates the number of cards with pre-modern format, ruling text "This is a triggered mana ability" that do not have multiple faces.
do not have multiple faces refers to side IS NULL
SELECT COUNT(T1.id) FROM cards AS T1 INNER JOIN legalities AS T2 ON T1.uuid = T2.uuid INNER JOIN rulings AS T3 ON T1.uuid = T3.uuid WHERE T2.format = 'premodern' AND T3.text = 'This is a triggered mana ability.' AND T1.Side IS NULL