What energy is used with a 5000watt oven being used for 30 minutes?

Well, it's an easy enough math problem, so I'm just going to tell you *how* to do it.

1 Watt = 1 Joule/second

5 minutes = 5*60 seconds

Multiply so that the seconds cancel each other out. This is simpler to just do with dimensional analysis than to try to evaluate it in separate steps.