Magic the Gathering simple damage question
If you have a 6/4 Craw Wurm blocking a 5/3 Bloodrage Vampire, then both creatures will die after combat damage is dealt.

In combat, after attacks and blocks have been declared, combat damage is evaluated all at once (except when dealing with First Strike or Double Strike, but that's not relevant here). In a situation like the one you have here, with one creature blocking a single attacking creature, each creature deals damage equal to its power to the other simultaneously. Then, after the damage has been dealt (or at any other time), if any creature has taken damage greater than or equal to its toughness, it dies.

In this particular situation, the Craw Wurm deals 6 damage to the Bloodrage Vampire, and the Bloodrage Vampire deals 5 damage to the Craw Wurm. After this, the Craw Wurm has 4 toughness and has taken 5 damage, so it dies. And the Bloodrage Vampire has 3 toughness and has taken 6 damage, so it dies.