Answer:
Karina, the new student body president, was previously the class treasurer
Step-by-step explanation:
Additional information like," the new student body president," should be surronded by commas. You can figure out if a piece of a sentence is additional information by taking it out, if the new sentence is still a complete sentence then that the part that you took out is the aditional information. Ex: Karina was previously the class treasurer. This sentence can still be considered a complete sentence because it has a subject, verb, and an object. Hope this helps! Let me know if you have any other questions!