Well if you can roll any number on the first 2 rolls, your equation can be written by the desired outcome over possible outcome. So for toss 1 you get 6/6 same for toss 2. Toss 3 is different because you want a 3 or 4, so you have 2 desired outcomes. So you get 2/6 and for toss 4 you have 1 desired outcome, so you get 1/6
You now multiple everything together and you get 1/1 (simplified from 6/6) * 1/1 * 1/3 (simplified from 2/6) * 1:6 which would give you 1/18. That is 0.05555555 repeating)