Science Buddies: "Ask an Expert"

I am doing a science fair project on dice rolling probability. I have a D-6 (six sided dice) and a D-12 (twelve sided dice). I rolled the D-6 100 times with my left hand, my right hand, and then cupped in both. I did the same with the D-12. After recording the numbers and then adding up the sums of all the added rolls, I repeated the process but with rolling both die at the same time. I am trying to record the probability of rolling a 6 with the D-6 once and multiple times in a row, and then the same with the D-12 but with 12 and then the D-6 and D-12 together to make an 18. How would I figure out the probability.