C , because there was 121 people in total which that is the total amount and then there’s 12 round tables and you are trying to figure out the number of guest seated at each round table which that makes 121=12n and since there was 13 people already sitting at a rectangle table then they don’t count so basically it’s 121=12n -13 . Because the people at the rectangle table don’t count anymore more because they are seating down in the rectangle table. And you just need to find out how many people need to sit at the round tables since there’s only 13 people sitting at the rectangle table. Hope this helps !
