Help me out please. (Math question-Probablities)

Right, so I've got an upcoming exam tomorrow, and I just found out I'm stuck on probabilities (Not sure if that is what it's called in English).

Anyways, the question goes like this :

Troms skiing facility got 6 menn for NM in skiing. 2 of them are under the age of 20. It's a 4x7,5km lap, and they are going to pick 4 "runners(/skiiers)".

a) What's the probablity for that NONE of the 2 under the age of 20 does this?
b) What's the probablity for that minimum ONE of the 2 under the age of 20 does this?
c) What's the probablity for that EXACTLY ONE of the 2 under the age of 20 does this?
d)What's the probability that the skiier hit at least 4 of 5 targets with 5 shots.? (Hitting 1 target = 90%)

If you could explain your answers, that would be great.
I will most likely understand it, if you just set it up correctly.

(Not even sure if I've been trying the right formula :
X=x (n) p^x (1-p)^n-x
----(x) (<- not n divided by x)


OR if you could do :

Statistic over football matches in 2005 showed the probabilities for home victiory (H), tie (T), away victory (A).
P(H) = 0,45, P(U) = 0,29, P(B)= 0,26

a) What's the probability that ALL the twelve matches ends with home victory?
b) How big is the posibility that the 6 first ends with home victory, and the next tree tie, and the last tree with away victory?
c) Probability that there won't be an away victory? (Assuming you can just take 1-a)