All of them.
I don't know how to summon Slifer before he's able to summon Ra without killing him.
The 4000 Damage is possible I guess, but same problem as above.
The 1000 LP is also a problem, I assumed to not summon anything until my LP are at/under 1000 LP, but he always kills me. His usual monsters are too weak so they can't destroy mine, but as soon as he pulls Ra out, I lose.
It feels to me like you just started playing recently and lacking lots of nice cards. In that case, don't rush it. Get better at game, get stronger cards.
Then you can solve those missions with ease.
I'll be here time to time. If there's any specific question and I see it, I will answer you if possible.