John is playing a board game that uses a pair of number cubes with sides numbered 1 to 6. To find how many spaces he can move on the board, he adds the two numbers he rolls. The possible sums are 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, and 12. a. Are all the sums John can roll equally likely? Explain your reasoning in detail.