If so, I don't understand why you included #4 and then #5. They are the exact same thing. Also #2 and #6 are the same thing.
Hopefully you can see that rolling 3 dice, the minimum total is 3. So the probability of getting 3 or more total has to be 1, or 100%.
There are (1/6)^3 ways to roll the dice. Only one of these: (1, 1, 1) results in a total of 3. Therefore the probability of getting total of 4 or more is 1-1*(1/6)^3 = 215/216 0.99537.
#1 and #3 are a little more involved. I'm not going to derive them unless you confirm that you are indeed trying to derive the values in parentheses.