The use of "la"?
Solution 1:
You are referring to the use of la as an exclamation. According to M-W:
- interjection chiefly dialect —used for emphasis or expressing surprise
Interjection la (from Wiktionary)
(obsolete) Used to introduce a statement with emphatic or intensive effect. (archaic) Expressing surprise, anger. etc.
- 1811, Jane Austen, Sense and Sensibility, vol. III ch. 2: “Oh, la! here come the Richardsons. I had a vast deal more to say to you, but I must not stay away from them any longer.”
Etymology: from French la, Italian la.