Tax Year Prior to 2020: How to file state taxes for an LLC working with out-of-state clients?

I am a single member LLC, registered as an entity in PA. I have two clients that are from New York that have me signed on as an independent contractor for their companies. Due to the nature of my services (photography/videography/social media management), I sometimes travel to New York to meet with these companies or take photos/videos for them, while other times I work remotely for them in Pennsylvania. 

 

I am unsure what state taxes to file for this income since my work is done about 50/50 in-state and out-of-state for these specific clients.