How long do you cook a beef and at what temperature?

Depends WHAT beef??? Oxtail requires4-5 hours proper cooking time at a simmer of medium heat.
Roasting a leg depends on the weight.
Using a cooking thermometer is essential to maintain correct temperature.
Best cooking temp for leg of beef is a low temp275 -325deg F as this reduces shrinkage and prevents the meat from drying out.
Here is a rough guideline below: Rare Medium Well Done1 kilo (2.2 pounds)30 minutes45 minutes60 minutes1.5 kilos (3.3 pounds)45 minutes1 hour &10 minutes1 hour,30 minutes2 kilos (4.4 pounds)1 hour1.5 hours2 hours2.5 kilos (5.5 pounds)1 hour,15 minutes1 hour,50 minutes2 hours,30 minutes3 kilos (6.6 pounds)1 hour,30 minutes2 hours,25 minutes3 hours3.5 kilos (7.7 pounds)1 hour,45 minutes2 hours,37 minutes3 hours,30 minutes4 kilos (8.8 pounds)2 hours3 hours4 hours4.5 kilos (9.9 pounds)2 hours,15 minutes3 hours,25 minutes4 hours,30 minutes5 kilos (11 pounds)2 hours,30 minutes3 hours,45 minutes5 hours

Its depend on the part of the beef meat. and how you will cooked it. its all depend.

if you need roast the beef to be welldone it must cook45min at180c... 

a/b  75  selchias

There three ways to cook the meet, grild, boild, or frid.
In each way there three steps, rare, midum, or well done.
In all cases you can not tell exactly how long it will take to be cooked.
That depends how you feel it and see it, is it cooked the way you need.
Feel it with a knife or a fork.
Look at it is it the way it should be.
To cook you haveto use your emotions and senses.
Just depemd on Alla and do it the way you like

By way as you like cooking you if you cook Shui or Girl all this time and at a certain temperature