GURPS Dungeon Fantasy 19: Incantation Magic

[Tinman]

I have a question about stacking spells (P.21-22):

If I have a buff that gives me a +2 to DX and I:
A) Have a buff that gives me +3 to knife skill. Q: Does it give me a +5 or only a +3?
B) Have a Fireball spell with a +3 to hit modifier built in. Q: Does it give me a +5 or only a +3?

Thx