How much protein should i eat to gain muscle ?

You dont want protein only after a work out. If you are wanting to gain muscle then you need it in pretty substantial amounts every day. A good rule of thumb is a gram of protein per pound of your body weight. Also you are going to want quite a bit of carbs they are another key in gaining muscle. Remember you don't actually gain muscle while your working out. You are just breaking them down so you need the protein to rebuild them. That is why you always need protein, and lots of it.