Wikipedia says more like 11%, but it’s pretty complex. NPR produces programs that local stations play, and pay for. So while you might hear someone say they’re listening to NPR, they’re listening to a “member station,” that is paying NPR. They might get some money from federal grants, some from the corporation for public broadcasting, which is federally funded, some from member stations who get some federal grants. So I’m not sure if all the info you’d need to figure it out completely is public. I assume corporate sponsorship beats out federal funds by quite a bit though.