сумма выпавших очков равна 7.

Let B be the event that the sum of the outcomes is 7. The outcomes where the sum is 7 are (1,6), (2,5), (3,4), (4,3), (5,2), (6,1). There are 6 such outcomes. We want to find the probability that the sum is 7, given that the sum is less than 7. This is impossible, so the probability is 0.