To get a sum of eight the first die must be 2 or greater and the second die must be one specific value that makes the sum equal to 8 with respect to the first die.
So the probability of Donna winning on her next turn, rolling a sum of 8 is:
In the question it says "the intercept of 6" which means the equation has to have +6 in the answer, and there is only one answer choice containing that.