Ok, in the oven its usually 180 C & 60 mins for every kilo of meat.

So whack yours in for an hour and then check it after that by sticking a knife in and if it comes out bloody etc, then keep it in there a bit longer.

Hope that helps, it really is easy, even if the first time is daunting....(I didn't cook roasts until a couple of years ago and now I'm an ace!)