How Do I Politely Stop My Coworker from Constantly Interrupting My Work Without Hurting Our Relationship?

I need some advice on a work situation that’s been driving me up the wall. I’ve got this coworker who’s super nice, but they keep coming to me for help with small tasks—questions about spreadsheets, quick favors, or just wanting to chat. It’s happening multiple times a day, and while I don’t mind helping once in a while, it’s totally throwing off my focus. I’m falling behind on my own projects, and honestly, it’s starting to affect my mood—I feel stressed and distracted all the time. I don’t want to come off as rude or damage our working relationship, but I need to regain control of my workday and actually think straight. Has anyone dealt with something like this? How do I set boundaries politely without making it awkward?