Bonus weapon by quests

[nana]

How can i make this thing:

1.- I have a sniper + rudrabow

2.- Sniper  makes "owls eyes bonus quest"

3.- Sniper recieve +10 dex +30atk 

4.- sniper makes "double strife quest"

5.- Sniepr recieve +10% more damg on double strife +10 vit

At the end of this 2 quests sniper have both bonus, in that char

+10 dex +30 atk +10 vit +10% more dmg with ds

:S

thanks in advance =(