Probability Application help

Hi,

I'm revising for my Maths exam on Tuesday and I really need help with this question:

*Three letters are chosen at random from the word "HEART" and arranged in a row. Find the probability that:*

a. the letter H is first

b. the letter H is chosen

c. both vowels are chosen

I think this is how you work a. out:

HEART has 5 letters, so 1/5 = 0.2

I'm not sure how to work b. and c. out though, I think it needs permutation and/or combinations but I can't work out the correct answer.

Any help would be greatly appreciated, and I'm sure I'll have more questions to come.

Thanks,

Dru