Ethernet Adapter

I have a "wi-fi box" as I call it (probably a modem). I also have a LAN cable coming out of it and going straight into my router. My speeds are 60 download and around 8 upload. If I purchased a 100mb max ethernet splitter and plugged it into the Lan port on the box and the splitter side into my router and pc, would both devices receive that speed? Or is it combined, where both would get 50?