Since I don't know LaTeX that complicated, I will tell you the probability of rolling 0, 1, 2, and 3 heads.
When you roll 0 heads, that means you can't roll a head each time, or (12)3, which equals 18.
When you roll 1 head, that means you roll HTT, THT, and TTH. The probably is still the same, but we multiply by 3 for each ordering, for a probability of 38.
When you roll 2 heads, we can use the same logic to get 38 again.
When you roll 3 heads, you get a head each time, or (12)3=18.
Hoping this helped,
asdf334