If 3 appears on the first die, then the sum of the numbers on the two dice can be 8 only if 5 appears on the second die. The probability of rolling a 5 on a single die is 1/6, so the probability of rolling a 3 and a 5 on two dice is 1/6 * 1/6 = 1/36. This means that the probability of rolling a sum of 8 when 3 appears on the first die is 1/36.
